5mile possibly. Motorcycle trader, and check your area.
I tend to disagree with "they need serious work". Some do, yes, but not all. What it takes is knowing what to look for when you buy.
You need to know what type (sport or utility) you want. What cc range, ask about the maintenance history and if they have records of it. Narrow your choice down to one or two brands. Come to places like this and see what reviews, problems and fixes you find for the model you want. Check prices on NADA and locally to see what range they're selling for. Make sure you see it in person, some may let you ride it, others may not. You should at the very least hear it run. Take your time, there are a lot of good used quads out there and some good deals too.