Here's my criteria for buying a FW:
Well first off- that it works!!
Intact decals- the detailing is so pretty
Bakelite pedal
Case in good condition
Owners manual and attachments.
No cord rot, etc.
Bobbin case- very important b/c they can be pricey.
Black FW are more common, the white ones were made between 1964-1971 (somewhere around that time. They do not have the decals) but are very nice
The 221 is the most common for both.
The 222 is rare- it comes apart for doing sleeves etc.
Hope this helps! I'm sure others can add to this.
Mine was 212.00 and had all that I mentioned plus had been completely serviced but that was a bonus, I would have bought it anyway. They are easy to maintain!