Update: My supercard and superkey came yesterday. I seem to have made a mistake. The sd card I showed was a normal sd card.
Here's a link for a 1gb sd mini-$30-
http://www.buy.com/prod/PATRIOT_1GB_...202755519.html
I noticed that my normal sd card was too big and now I have to wait for 6 weeks until I can test, due to me leaving. It should work though.
Finally, Boomerang, what are you talking about? Why would it be better to spend $100 than $82?
Finally, the supercard is all that's needed for normal homebrew, and for gba rom homebrew. All the superkey allows you to do is play ds roms. The supercard is the more expensive of the two, but it is technically the only thing needed to play "homebrew". It just can't be used on it's own for ds roms.