Tell us exactly what you are looking for. And what you want to do with it. You got lots of good advice above. Those guys pretty much know used guns and what they are talking about.
If you find a good deal run it by the group here. I don't think anyone here will step on your toes and buy it out from under you. This is pretty much a good group of guys, and will help you out.
You should be able to find a decent rifle in the $150 or so range. Cayugad amazes me at some of the deals he finds. And I know if you ran a deal by him he would never buy it out from under you. The guys can be counted on. So let them help you.
I know alot about MZ shooting. And they teach me things all the time. And they are more than willling to do so. Good luck in your search for a nice rifle. Tom.