For that money, you've got some choices. If a TLR will do the job, a Yashica 635, 124G, etc. is very good, or you might (with a little patience) find a Rolleicord in that range.
For folders, if they don't have to be cheap, a Bessa (not the 35mm rangefinder) is a very nice 6x9 cm folder with an excellent lens, coupled single-window RF, and sometimes in your price range. Or for a good bit less, a Moskva-5 has a two-window coupled RF and a Tessar-class lens, and some come with a format mask to let them double on 6x6. I owned one of these for a while back around 2002-2003, and should have kept it.
EDIT: Okay, didn't read closely enough -- for SLRs, there's really only one that I'd recommend that might land in your price range: you can, with a little patience, get a "from Japan" RB67 with one lens and one film back, possibly in need of light seals, for around $400. If you can, get it. Additional lenses are quite reasonable, film backs likewise, the cameras are still repairable, and they're completely battery free (no electronics to crap out without warning). Only major downside is they're heavy -- but I think that's likely to go for any MF SLR.
I've got one, and I love it -- it's not a walking around camera, by any stretch, but it was a serious studio camera for decades.