Sometimes you might get lucky on Craigslist. I've seen all kinds of machines and all kinds of prices. I got a "newer cheap" Brother for $7.50 off CL and I've seen machines I wouldn't want in my house for several hundreds (nasty rusted boat anchors!!).
Believe it or not, I've had the best luck with machines at pawn shops and estate sales. The last machine I bought was from a pawn shop: a Necchi for $15. But I got a Pfaff at an estate sale for $50 that just sold on ebay for $200! I was shocked! I wish I could find out how much they cost 30 years ago when they were new! Sounds like I sold my machine on ebay, but I meant someone else sold the same kind for $200!
It would have to be a pretty special machine for me to buy it from a thrift store. I only see the "This is old, so we want $100 for it" ones there. And I'm thinking, "wow, someone GAVE that to you!" and I assume that something is wrong with it, which is why they donated it. The one time I did buy one, it didn't come with the foot pedal. I gave it to a co-worker and she bought a pedal for $20 or so, so that worked out well.
If you're wanting to quilt anything larger than a pot holder (tongue in cheek there!), look for one with a little more throat space. My Pfaff has 7.5 inches from needle to arm and 5 inches up the arm! It makes a big difference from my 6x5 Janome ($40 from a pawn shop!!).
good luck!