Craig's list is your friend. Just keep an eye out.
Many of the new "cheap import" winches are surprisingly good. I'd seriously look at either the smittybuilt xc8000 (I've had one and was very impressed with it) and harbor freight's "badlands" 9000 or so (I wasn't impressed with hf's earlier winches but the new one appear to be improved and on par with the smitty). Either of these can be had for around $300 give or take if you wait for the right sale.
Course there are a ton of other brand winches out there. Many are re-badged version of the same winch with different colors or graphics. I shy away only cause they are more unknown and sometimes more $$ compared to the smitty or hf ones that are more known.
I've never cared for milemarker, ramsey is good, but slow so they have never been my favorite. Hard to go wrong with a good warn unit, the m8000 is very common and a good work horse. Not fast but reliable. Just be warned, you can get them new for between 4-$500, so I wouldn't pay more than $200-$300 for a used one, as a mater of fact I'd serious think about paying more than 1/2 of new for any used winch unless it was in excelent shape or upgraded. Significantly less if it need work (like missing cable or bad solenoids). Figure $50-$100 for new cable, you'll be into solenoids for $50-$100 as well assuming you can do the work yourself.