I don't know about Proform, it may be OK. But IMO your probably better off with a secondary line from a major manufacturer (BTW - STAY AWAY from CAL!!).
The 700 series is a nice tub, I don't know where you got the impression that they're not that good. But keep your options open ... go to Coleman, they should have a tub at about your price range along with Artesian Island series, D1 @ Home series, Marquis Everyday series and Master Down East series. Hot Springs dealers do have lower lines, I would imagine there's one in your budget. And there may be others that I didn't mention.
From what I've read, there could be a problem with local manufacturers or lower quality spas and getting parts and service.
Take your time and look around, you'll find a nice tub.