I wish I was willing to spare mine. My 180 is not in very pretty cosmetic condition anyways (BGN from KEH and it shows, but it works fine).
Speaking of KEH, I would check there. I haven't priced the 90 because my RB came with one, but I only paid about $50 for my 180 C and other than the really bad paint job a previous owner attempted with what appears to be nail polish, it's perfect.
If you don't have luck here, check there and you can find a deal.
Good luck, Shawn.
-James.