What you want to look for is the basics. Make sure it can do a good straight stitch. A zig-zag stitch is helpful (it helps make bar tack stitches) If you can find one that can change the speed at which the feed dogs advance the fabric that is a helpful feature.
Brother, Singer and White are all good brands.
HE is right. Check the sewing shops for refurbs. I found mine at a yard sale for $5. It worked (and still works) like a champ.
Hope that helps.