In the UK, you could maybe get a beater M3 for $500 or more like $600, no lens, so maybe if you really hunt around, you could find one. Also there are the Bessa models of course, again you may be able to get a beater R2A within your budget.
I think you should still consider medium format, maybe the Bronica RF models. The cheapest medium format camera will blow away any Leica 35mm camera for quality, excepting Holga etc.