Yeah, I would pass this up. Here are few observations:
An above ground pool has it's share of maintenance too. With your yeard, you'll need to hog it out, wire it up and install a heater. Any pool maintenance is just as expensive as owning a Race Car. With trailer.
An in-ground pool costs, currently (My friend got the quotes last week) $25-$60k to install. Don't even think of it.
A hot tub, however, is far superior. It has the same maintenance schedule, but since you aren't using chemicals by the gallon-full, your costs are down. With modern (Read: post 1994) tubs the covers and side insulation is so good that the heater won't come on at all. Also, your insurance goes through the roof with a pool, whereas it doesn't with a hot tub. You also don't need zoning and permits to install a hottub in your area - And if there is a roof over it (Like your lower porch in back) then you'll have an easier time insuring, maintaining and ultimately keeping it.
Hot tubs only get better in the winter. However, since K-Chan is really thin, she'll prolly want the water a lot cooler than you. So don't expect to occupy it at the same time. A guy your size might appreciate the full 108-106 degrees, but I can only stand 101 for about 25 minutes. She'll have a hard time with 100 degree water for more than 10 minutes. I imagine you'll both be 10 degrees apart, and to get a tub to those temperatures takes a day or more.
-> Steve
I suggest a small two person tub, new with warrantee and service for the back porch. The smaller it is, the easier to adjust it's settings and maintain it's chemical levels. At most it's going to run $5000 beginning to end. Used, a lot less. Plus, we can transport it in pieces if you find it used. The nice thing about a smaller one is that people are selling them to buy bigger ones, not selling because they aren't satisfied.