Are anime conventions a rip off ?

My question is focused on the retail section of the conventions.
You can basically purchase anything retailers sell at conventions for half the price online.
I guess since my taste in anime differs quite a bit from the mainstream I really don't get to enjoy the convention experience. So if you are not into most of the events being offered it's basically not worth it.

Sometimes you can get a great deal in the dealer's room of a convention in the last hour of the last day. Sometimes the dealer will slash prices, because s/he doesn't want to haul it all back home.

I never taught about that. It's like a double edged sword though, if you are attending for one day. The earlier you go the better the selection the later you go the better the price.

Does anybody have an encouraging story about a last minute bargain at a convention?

I mainly go for cels. I've noticed that many dealers have top notch cels only at cons and not their website, which is definately an incentive for me to fight the crowds in the dealers' room.

Other than that I get a few books and anime t-shirts.

The CD's and DVD's are still too pricey for me.

Plus, it's hard to find cd's and DVD's that aren't ripoffs. Too many sell only Sonmay and other cheap reproductions.