It really depends on what you are looking for. It you want the refurbished, repainted, and as they say about cars, "All cherried out" then you are looking at a price in excess of $1,000.00. It took me years of checking quilt shops, yard sales and such to figure out I did not want to pay over $300.00. Then thru the QB I found shopgoodwill.com and Ebay. You read the review and also about the seller and make an offer. I ended up with 3 - 2 under $200.00 and one at $300.00. I felt one would be a good parts machine in case I needed one in the future. But all three were in fine condition, 2 were shipped with wonderful packing and the other was at the local Goodwill shop and I was able to pick it up.
I still check Craigslist from time to time to see what is out there - but before by the time I called it was either already sold or they wanted way too much money.
There is no set price - you have to figure out how much you want to spend and maybe talk to a LQS to find out what they sell for in the area. Or maybe your local Goodwill can tell you what they would charge if they got one in. Because they really are priced by what the local market.