Old Singers are really easy to work on yourself. Our virtual machine shop has a great tutorial that Billy did.
Featherweights vary in price, usually from 200-300, although people have been lucky and gotten them for less.
The 221 is in this price range, the 222 is a lot more costly, has the detachable piece, and I never heard of a 223.
Check Ebay for going rates.
Good luck!