I bought my first FW from the owner of my LQS for $250.00. It is a 1948, definitely used, but not abused. I was thrilled with the price, as the machines I had seen from a dealer at a show were quite a bit more expensive. To be fair, the dealer's machines had been professionally serviced prior to sale. The machine I bought runs beautifully, but had not been serviced for many years.
About 2 months after I bought my first FW I almost literally tripped over a second FW at a yard sale where everything looked as if it came out of a tool shed, not a sewing room. Actually, there was quite a bit of sawdust in the case, maybe some misguided person was storing it in a tool shed! After checking for a bobbin case and plugging it in to see if it ran I quickly paid the $35 it was marked and got out of dodge before anyone thought better of it. I cleaned it up at home, it runs beautifully and now resides at my daughter's house.
If I were still looking for another FW I would be checking thrift shops, antique shops and Craigslist. Local is the key - I would want to look at the machine, make sure it runs, has a bobbin case, etc. I would avoid Ebay at all costs, as I would not necessarily trust the seller to pack it properly for safe shipping.
You will find your FW, perhaps when you least expect it.
Happy Searching!