as far as what tub goes for $2500 used, I don't recall, actually....but they've got everything from an older Viking, to Jacuzzi to Vita to Esther Williams and more on the floor.....Some are better names than others.
I don't know what other people's experiences may have been, but I would recommend against Viking. One of my local dealers carries them and I looked them over seriously when I was first considering, and they seemed very poorly constructed - the shell had a cheap look and feel, the jets were flimsy, and it didn't seem to be insulated well at all, just a 1-2" layer of foam on the underside of the shell. Plus, the largest model that they carried (93" x 93" if I recall correctly) was only $4000 brand new, so it'd have to be pretty recent for $2500 to be a "deal". The dealer refused to show me the warranty, so I can't comment on that aspect.
I made a post about a year and a half ago in another forum asking for opinions on it, only got one response from a guy who had had one for a couple of years and said it was "ok". My main concerns were reliability and cost of operation, both of which I concluded were likely sub-par. Just my $.02, I'm sure I will be promptly contradicted if others feel differently.
I would have jumped at something like East TX Spa has (used HS in the $4500 area) in a heartbeat. I like the Jacuzzis too, if you could find a recent model with a warranty.