What I didn't mention in my above post is that I looked on/off for 2-3 years at hot tubs on C/L, mostly the free units, or for a few hundred bucks. I wasn't ready due to some planned construction so I took my time. I went and looked at several and talked to a lot of knowledgable owners and some were hot tub repair guys wanted to clean out old hot tubs they were gifted over the years. The older ones with wood sides don't hold up as far as looks go as well compared to Yr 2000 and newer units. Prices are all over the place, there are dreamers and people who want a relatively new H/T out of their site asap and will give it away. Overall, you're probably better off finding one for $500-800 that doesn't need anything and have a relatively new cover, and if you keep a sharp eye out and have the $$ on hand, those good deals DO come up fairly regularly in our area.
You need to strike fairly quick when you see them, so, work out a hauling strategy in advance. A snowmobile or ATV trailer works best (just tilt the tub up on end, tilt the trailer up to meet, strap them together and lower the trailer and H/T together - BINGO), but probably the most convenient would be to make a basic wood skid frame to go under a 8x8 H/T and cut some 1.5" PVC to 1' lengths and use them to easily roll onto the back of a rollback tow truck which you can get there pretty quickly and probably cost less than $100. There are a bunch of youtube videos on moving a H/T. Don't do what I did and put a doozie in the back of a Pickup! (I can manage it with a skid loader too). Also learn what brands the local dealers around you sell and stock parts for because there's a good chance you're going to need an unexpected part some crazy weekend when you don't have time to wait for mail order (like when it's -20F outside).
So keep your eyes open, great deals are out there. It's important is to learn what style you prefer in terms of features and seating arrangement. There are round ones, triangle shaped, Octagon, 2 person, 5 person, 7 person, with lounger seating, foot masager, waterfalls, LED lighting, air bubbles, bench seating or individual bucket-style seats, stereos, CD players ...and many more features. I talked to a lot of owners, it was kind of a fun process because it truely *is* a buyers' market in the low price range. I learned that what seems like a gimmick to one person others love and couldn't live without. Don't rush it. Even if you lose out on a deal, another one will pop up again soon.
If you really want to go in-ground, I would think it would make more sense to settle on a certain type of H/T and look for a complete one for free or almost free, then disassemble it with all the plumbing intact and put the shell along with any new framing you make into your in-ground mounting location. Make provisions for a repair strategy like mounting the pumps, heaters and so on in a remote above ground location. Maybe have special framing and hooks so you can hoist it out of its burrow with a skid loader if and when you need like if you have a major plumbing issue and need to get at hoses or connections. Love to hear what you're thinking.
