Woah woah woah... 800 bucks to change the rings? Sure that might be an ok deal- but you can get a whole B18B for 800 buck. If you know how to do it, then do it. You might bitch and moan about it now, but once your done- youll be glad you did, and youll be $800 richer for it.

Edit, sorry- i just noticed its a B18C.