First post so flog my newbness if this isn't correct, but dumping goods a cheap computer parts seller has a powerkit for the gameboy advance sp on sale for 99cents.
Shipping kinda of kills the deal. But if you are buying something else then I guess its OK. I've bought from them before, just a couple of NAKI spiderman gamecube kits (came with a controller, case, and memory card) for $2.99. They are all sold out of these now, but you can get some good cheap headphones for $2.49:
I bought about 10 of these headphones cause I hate when headphones (even good ones) get worn out and only one side is working. So now I have alot of back up headphones. These are pretty good, I'm still on my first pair. I gave some to my brother and sister and they seem to like them too.