210mm lenses for 4x5 are plentifull on the used marked. It all depend on what you are looking for.
Is it a modern plasmat then there are lots of choices, Fuji, Schneider, Nikon and Rodenstock all made excellent lenses and there are very little difference between them. All will be mounted in Copal 1 shutters which are very reliable shutters.
Fuji lenses seems to go for a little less than the rest but they are excellent lenses. I sold a 210 5.6 last year after getting out of 4x5 and it was a super nice lens.
200.00 if you are patient but no more than 250.00$ for a very nice lens these days.