I bought mine on-line. The dealer wanted an arm and a leg, I think I paid $69, but I bought some other things for my other cars too, to save on the shipping.
Thank God you got yours off without stripping those bolts, that was the problem I had. Once the bolts broke off then I had to cut the valve off, grind down the broken stubbs and then drill and re-tap the holes for some other bolts. Either that or replace the whole canister at about $300 on-line $500 at a dealer.