If you just want games and homebrew, no music or videos or anything like that, 2GB should be enough.
Remember that homebrew is very small, mostly around 1mb.
However, if you want to basically turn your DS into an iPod w/ tons of music and vids, you'll probably need more space.
There is a new product called the "m3 DS Real" on
Dealextreme.com for 34.90 and free ship
It is basically a G6 Real clone for much less. However, it is different from the g6 real in that it doesn't have built in memory; it uses microSD cards like an r4. But it can support SDHC!!
Just putting my two cents in