I bought a used hot tub from a person I knew. It needed work and I was going to do it myself to save some money. Five years later it is standing on its side in my back yard, barely touched, still not usable. It had only 1/2" of insulation sprayed on the shell, a wooden structure and plumbing and electrical issues.
I've given up even attempting to repair it, I bought a new (off the showroom) 6' dia Bullfrog hot tub and could not be happier with it...except when I am sitting in it and I look over at the wasted $700 eyesore standing like a monolith mocking me from across the yard. I just write it off to a hard learned lesson and figure that the couple I bought it from needed the money more than me at the time.
I would recommend checking out some budget models from reputable dealers some of the cast plastic models can be pretty decent for a few thousand dollars.