The price of the nintendo DS toptoy cartridges has come down to circa $7 now and looks to be a bargain. However, be aware that there seems to be an unacceptable level of failures with these cards at present - I have bought 2 of them over the last 2 weeks and they both stopped working after a day or 2. Tried all the fixes listed on the internet, but it's deffo the cartridges.
The internet has lots of complaints about these things failing and if you look close you will even see comments on the Deal Extreme site. I hope to get them replaced but the customer service at DX is poor, so we will see.
You have been warned!