We spent $19,500 for an 18X36 inground vinyl and we added a slide and a diving board and a larger concrete patio so after it was all said and done with inspections and hiring electrician and county people it came to around $22, maybe $22,500. And it took him about three months to complete... it should have been done in 6 weeks.
Two things, the first being, the guy that did it was the step father of a buddy so it took longer and he kind of tried to half A a few things, for example the cover and the auto cleaner.
The second thing, my son swims every single day and he has his little friends over all the time and I would pay pretty much anything to keep my kids entertained, plus I get to have my Mommy friends over and we break out the margaritas, it's been a very good thing for us. But be prepared, when you tell people you are putting one in everyone will say things like "We just walk to our community pool, it's like all the fun with none of the work" or "I have friends that never ever use their pools, it's a big waste of $$$" People can be so stupid.