It's totally going to depend on your area.
For instance, there's a thread right now where people are talking about the price of 301s.
http://www.quiltingboard.com/vintage...0-t223834.html
I can tell you that in my area, they don't go for nearly those prices, but others will say that the price being asked by the craigslist ad is a steal. If you can, besides Candace's suggestion of completed auctions on Ebay, see if Craigslist, or if there's a Used<yourtown>.com try there too, see if anyone has anything similar listed.