If you have completely legal homebrew games that you want to play on your Nintendo DS, then you might want to check out the M3 DS Simply Complete 1GB Kit. I'm sure that none of you would actually attempt to play pirated games on your DS, that would be unethical.
We've covered similar products before. However, the M3 has one distinct benefit over the DS-Extreme. Removable storage. The memory is stored on an included 1GB microSD card that can be easily switched out with other, larger cards.
A quick online search yielded prices of around $39 for the M3, which makes this one of the cheapest solutions we've seen yet.
M3 DS - Play Homebrew games on your Nintndo DS [via coolestgadgets]