Go to:

http://www.globalcomputer.com/

Do a search for "radeon 9550"

You should find the following:
Sapphire Radeon 9550 / 128MB / AGP 8X / VGA / DVI / TV Out / Lite Version Video Card - $29.99.

Shipping for me was $9.

It's not listed as "in stock", but "ships in 24-48 hours". I've never bought from these guys before, but I think they're affiliated with tigerdirect so hopefully they're OK.

Good luck!