I don't know anything about pool installation in ND but....you really, REALLY need to get a couple more estimates, preferably from guys not sharing prices with this contractor. Have you checked with the cost of what you want with the internet companies?

The liner itself, even custom made, is no more than $1100-$1200, maybe $1500.. Installation shouldn't be much more than liner.
Auto cover for $11,000??????? Which you will use in June, July and August, and either leave on all winter or replace with a $1200 safety cover. Given everything else I'm guessing it's about double what you should pay. Or more.

And $6800 for solar panels PLUS plumbing? What are they made of, Mother of Pearl? Are they to be installed on your roof or on ground stands? If you put in a gas heater for as much as $3000, $3800 buys an awful lot of gas--and I'm an advocate of solar panels, as I have them. The only solar systems I've seen for that much are the specialty ones that go in the attic near the peak and use the attic's heat.

If you are handy, you can do much of the work, especially since it's a vinyl pool that needs a liner anyway--ideal time to do a double bottom drain.