While many think it's too much work and expense to own a pool, I consider it very worthwhile. I spend as much of my summer as I can in the water!
As far as expense goes, pool season usually adds an average of $15-$20 per month to my water bill (I live in Tennessee). I can't be sure its true effect on my electric bill, as it is usually turned on at the same time as the a/c and I chalk most of the power usage up to that. Depending on the weather that year, I spend around $300-$500 per year on chemicals. Repairs do tend to be costly, but don't come up too often (knock on wood).
As for time and work, opening the pool is where most of the time goes. Don't ever decide to open your pool on Thursday and expect to be swimming by the weekend. I usually start opening my pool in early May, knowing I can safely make plans to have friends over for Memorial Day grilling and swimming. If you have amazing water flow and continuous free time, you could probably have it open in three days. I take my time about it.
In my experience, I don't ever recommend paying someone to open your pool for you unless they are contracted to handle your pool for the whole season. For upwards of $150 or more, they will do what they can in one day and leave you with a pool that still needs substantial work if you hire them only to "open". It takes time, but it's not hard to do on your own.
The first steps to opening your pool will vary based on how your pool was closed. A typical closing would include draining a few feet of water, closing the pipes and putting a cover on. In that case, you will remove the cover, open the pipes, and refill the water.
When removing the cover, you'll want to grab a helper. All the water that pools in the middle makes it very heavy. Ideally, roll from one end to the other. As you get closer to the end, the water would be heaviest. Try to splash the water over the edge if you can, as it will be covered in algae. If you have to let it fall back into the pool, trying to contain any leaves by filtering with a skimmer net. I've tried sucking the water up with a wet vac without success. There are tools available through pool supply catalogs that are designed for sucking the water off the top of the cover for easier opening, but they're awfully pricey for their once-a-year use. Just do what you gotta do to get the cover off, and be prepared to clean up a little sludge.
After the cover is off, remove any plugs that might be covering the filter baskets and open the lines. A picture of what your lines' on/off valves may look like is below. Don't turn the pump on yet.
As you can see, my pool has three skimmer baskets, and each valve controls a different skimmer. I have one on each side of the deep end and another lower on the wall of the shallow end. Your valves are probably all turned to the off position. Turn them all on and remove any plugs in the skimmer baskets if you haven't already. Then turn the hose on and let it fill all the way. You might as well go ahead and fill to nearly overflowing, as you'll have to drain some of the water as you clean. This is my pool immediately after opening and filling:
Pretty gross, huh? The grossest part to me is the realization that this is the water I will eventually swim in. It doesn't really get replaced, just cleaned. Still it does clean up nicely.
Next, make sure your skimmer baskets are empty of debris. Also check the filter that is right outside your pump. It will probably look something like this:
After you empty it, make sure you reattach it fairly tightly. It needs to be airtight, but not so tight that you can't get it back off or it makes the plastic crack.
Once you've got the pool filled with water and clean filters, you're ready to turn it on. Make sure the pump dial (mine is pictured below) is turned to "filter", then turn it on (usually by flipping a breaker).
There will be some churning and bubbling as the air is pushed out of the lines, but the filtering system should be functioning quietly and normally within 2-3 minutes. Now you're ready for your chemical attack.
As it gets closer to swim time, you'll be more concerned with the overall chemical balance of the pool. I've found that, to start, you just have to shock and shock and shock some more. While I don't want to endorse any particular product, I have found that I MUCH prefer shock that is safe to add directly to the skimmer line. Other shocks have to be diluted and dumped into the deep end, and for whatever reason, they just don't seem to work nearly as well for me as the ones that can go straight from the bag to the skimmer (remove the basket and pour the shock into the hole, then replace basket). To start this year, I used six pounds of shock (I have an approximately 30,000 gallon pool). This stuff is amazing. Here's the same pool about 45 minutes later:
And after about an hour and a half from initial application:
The water has mostly gone from green to blue! Now, we have to deal with those dark spots... mostly leaves but also dirt, tadpoles, etc. So it's time to vacuum.
First, attach a vacuum head and hose to your pole. Completely submerge the hose. I put the skimmer end of the hose up to the water return in the pool (where the water jets out) to force all the air out and fill the hose completely with water. Then attach the skimmer end of the hose to the skimmer, usually with some attachment end. Because I use my skimmer line that is on the wall of the pool (rather than one with baskets), I use an attachment like this:
This catches the bigger stuff like leaves so it doesn't go through the lines and clog them. At this point, the pump is still on "filter". You will need to turn the pool off and rotate the dial to the "waste" setting. Because you will have small particles of debris and algae, you vacuum to waste so that small stuff doesn't just keep recirculating back into the pool. Turn the pool back on, make sure the vacuum is still appropriately attached, and begin vacuuming.
Because you are vacuuming to "waste", you are continuously losing water. I always have the hose on, refilling as I go. Still, I drain faster than I fill, so I can usually only vacuum for about twenty minutes before I need to stop because the water level is getting too low. I then let the hose run for about two hours before I vacuum again. This is the main reason why opening takes so long: two hours waiting to be able to do twenty minutes of work. I usually do 1-2 vacuumings per day until the job is done.
For normal pool operation, you can't let the water level drop below your skimmer baskets. Otherwise, you're sucking air rather than water, and that will damage your system. For my pool, that means the water can drop only about six inches. When you're vacuuming to waste, you have to keep it even higher because you're going to have to follow up with "backwash" and "rinse". More on that in a minute.
As you vacuum, especially at opening, check frequently to make sure the line isn't clogged. You may have to pull some leaves from the bottom suction hole to keep things moving. You will probably need to stop periodically to empty your basket as it fills with gross stuff. Make sure to turn the pool off when you do, dump the basket, reconnect the vacuum, and turn it back on.
When your water level drops to about two inches above your skimmer line, turn the pool off. Remove the vacuum (hose and all) and empty the skimmer baskets and the filter up by the pump. Turn the pump dial to "backwash" and turn the pool back on. You should be able to see the water somewhere near the pump (I can see mine through the pump filter). Leave the pool running on "backwash" until that water begins to look relatively clear. Then turn the pool off and move the dial to "rinse". Turn the pool back on and let run about another 45 seconds. Turn the pool back off.
Vacuuming cleans the pool. Backwashing cleans the pool lines. Rinsing cleans the sand in the filter. All of them dump water from the pool. That's why you have to leave some water after you vacuum, so that you have enough for the backwash and rinse. Your water level is now probably fairly low, but as long as it is still above the skimmer line, turn the dial back to "filter". Turn the pool back on and the debris floating on top of the water should start filtering into the skimmer baskets. Leave the hose on to fill the pool back up as high as you can to prep for the next vacuuming session.
Repeat the vacuuming cycles as often as possible until the pool floor is clean. The pool will probably have a tough time of maintaining its chlorine levels in the beginning, so shock again at the first signs of any green.
When you get to the point of being within a week or so of actually swimming, take a sample of your pool water into your local pool supply store. You can use an empty soda bottle. Be sure to fill it up so they have adequate amounts for sampling.
Any pool supply store will run an analysis on your pool water for no charge. I highly recommend this over at-home test kits. They are more accurate and the professionals can tell you exactly how much and what you need to add to your water to make it safe for human skin. The products they will advise you on will also make your pool most chemically efficient. This isn't a bunch of upselling; listen to and follow their recommendations for your best pool experience.
After your pool is opened, you will need to keep it supplied with chlorine tabs and typically a weekly dose of shock. Take a new sample to the pool supply store every few weeks to keep everything in balance. Really hot weather uses chemicals faster. Rainy weather leads to more debris in the pool.
I love the timer I had added to my pool that turns it on twice a day, for 2.5 hours each time. Once the pool is opened and the timer going, I spend an average of about 30 minutes PER WEEK (usually while I'm in the pool enjoying it) doing the rest of the summer's maintenance. The rest of the time is fun and sun!