You can buy a new one for £279.00 so I'd make that a starting point - good nick second hand you'll be looking at approx £200 there or there abouts I would have thought...
I've got the Zoom MRS1266 (which you can't get anymore, been replaced by the 1608 I think).
These machines are fantastic, I've recorded all sorts of stuff with mine, the quality is awesome for what they costs and would be ideal for making top quality demo tapes etc and a damm sight cheaper than studio time... and with built in effects (some better than others), drum tracks (great for just laying something down to, you can always revisit it which is what I do) etc, if you're think about getting one, then do...
Have a bump on me