I agree that sometimes art supplies can get quite pricey! Though, that being said, I'd love for my canvases and brushes to be as cheap as you mentioned!
I recently picked up two SMALL canvases (a 5" by something and an 8"x10"), several small tubes of paint, a small carrying case, some brushes, a small pallette (the cheap plastic kind) and a few odds and ends, and it was a solid $240+! A lot of my brushes (especially ones from the small university-owned art store at my last school) cost at least $15-20 a piece while I'm sure I've spent a solid 10-30 for so-so canvases in the past (I saw a "sale" this week at the art store for a pretty large canvas...only $70! lol) I think around here, the small stores (which I try to support) end up having to mark things up a good bit just to make up for the small size of the town.
What's been said about quality tools being worth the money, I second. Just remember, the tools are pricey, but they'll last a very long time.
I'd recommend learning to stretch your own canvas. I don't do it as of yet, but I'd imagine it could save some money. Also, try to buy the best brushes you can and baby them. That way, you'll save in the long run (though it will be expensive up front).