Price is between you guys. I just suggested a possible source for arriving at a fair price. I do know they're hard to come by.
I called a local parts dealer to see if he could help you out, but he's also looking for one. There is a 6qt tank for a C85 on eBay - perhaps you could look into that one and see if it's possible to use it on your motor.
They do show up on Barnstormers from time to time.