For that kind of money, you could get a low-shutter-count, well-looked-after K5II (I see them going for $300-$350, and there's always a little wiggle room
). There's at least one I can think of in the Marketplace right now, I think it's $350 but has a crazy low shutter count - less than 1000 shots, if I remember correctly - and has obviously been extremely well cared for.
The K5II is a flagship-quality body, so a good example should last you a long, long time - and the image quality from all of the K-5 cameras is superb. The only sticking point is AF tracking performance, which isn't as good as some other brands' comparable models... but it works pretty well.
You might find a quite-heavily-used K-3 for that kind of money, too... But I'd rather go for a lightly used camera, personally