I'm going to suggest a different way to look at it, because I'm not sure these percentages are meaningful out of context.
(In my case, my pool was "free"...insofar as it was a foreclosure and there was about a 150% differential between what was paid for the property and its current appraised value on mere year later
...the cost of my pool today would also be higher than normal due to a variety of things its construction required from the original owners.)
So the way I'd look at investing in an in-ground (and I DID look at it this way actually -- and then decided it was smarter to just go buy a house that already HAD a pool instead of constructing one...)
1. Determine how long you intend to stay in that house.
2. Amortize the cost over that time and determine if that is a sustainable cost/eg. "worth it."
3. Forget about recovering the investment...too many people DON'T want pools, so you have a very specific clientele and that can mess with resale value
4. Consider it instead an "entertainment/consumable" lifestyle investment not unlike a luxury car or cottage or annual cruises, etc.
You will notice that if your answer to number 1 is "20 years" your construction cost, amortized, looks like pretty cheap entertainment. You will notice if your answer is "four more years" on the other hand, it's a little steeper!
If your answer is truly anything under 20 years in terms of question 1, consider going out and finding your "death house" as I call it now. You never know what you might find, but it's possible you'll end up with the pool "free" by comparison
That's what mine is -- the one that is one floor for when we're old and can't do stairs, large master, guest area not in main house, enough land, plan-to-die here...etc.