For me the biggie is to make sure there isn't any rust and that it has a bobbin case. If no bobbin case, knock $50 off the price right away as you'll have to replace it. Also make sure the motor works. Cosmetic condition isn't a huge concern for me. I agree with checking eBay completed listings, it will give a good idea what condition can command what price on the mass market. Attachments can be had for around $10-15, and replica manuals for $15 or a free download. If you aren't going to travel you don't need a case, or you can sew a bag. But all of those tags should play into the price. At this point I wouldnt pay more than $225 for one and it would need to be in excellent shape. They can be bought on eBay or goodwill for around those prices. If the cosmetic condition isn't grand, then i would say $175 is around the tops I would go, and subtract from there any missing parts. That's based on my area though. I won't buy one with rust,and won't buy one if the motor doesn't work. I would buy one that doesn't turn by hand, as I think I could fix it.