Sorry but I have to correct you there. It is very possible to find an SLR for £80, even £50, as low as £10 for some... because these are 35mm
film SLRs. Chris presumably knows this since he has looked at specific models.
Digital SLRs on the other hand are as you say usually more expensive.
If as I assume we're talking about film SLRs, "picture quality" is never an issue because the lens and film determine that. Some cameras may be better at auto-focusing or auto-exposure than others, but then you might be able to produce a better image using a 50-year-old camera and lens with no auto-anything. But since you say you want auto-focus, your options are basically any of the following systems... Nikon, Canon EOS, Pentax, Minolta. All of their 35mm SLR systems offer auto-focus with the option of manual focus. You can find a camera and lens combination within your budget for any of those brands if you look for used ones (especially on
eBay) and the lenses for any will also be useable on digital SLRs - Nikon, Canon and Pentax all have digital SLR systems and Sony took over Minolta's system. In other words you have plenty of choice.
P.s. I didn't mean to say the MZ-50 and MZ-60 are
that limited. Both of them will let you use auto-focus and will let you focus manually with auto-focus lenses. What they won't let you do is use
old manual-focus-only lenses - which none of Canon or Minolta's auto-focus cameras do anyway.