Whatever you do, get a 3-head machine, since 2-head machines are a pig to do record alignment on. That rules out all quarter inch 8 tracks, but then I would rule them out anyway on sound quality.
I briefly owned an Otari MX-5050 Mk III half inch 8 track before I got my custom Ampex 8 track half inch repro machine built. Otaris are better constructed than Tascams, I'd say. Has a built-in tone generator to aid with lining up, which is nice. All the pots are easily accessible from the rear.
Best of all would be a 1" 8 track of course, but your price range points to a half inch.
Good luck!
David Ollard
Thin Brown Line
Multitrack Analog to Digital Transfers