$495 is full retail price and yeah, it is for all 3 silencers. I think I got mine for around $450 at my dealer, though I have a good relationship with them. You may be able to negotiate with your dealer or find some deals on the Internet.
The catbypass (silencer upgrade kit) is $350 retail. So full retail for those two items is $845. Clamps I don't think you need as the existing ones will do. Gaskets you would need but I'm not sure how much they are sold separately, maybe at most $20-$30 for a set of three.
So everything for $895 is an average price I think.