Looking at buying R4 or R5 or whatever for a DS

[Heathen]

I dont have the slightest clue which one to get or where.

I legally own the games, but I hear you can fit like many games on one, which would be great for trips so I can leave my cards home.

Any help?

edited:
http://www.buy.com/retail/product.asp?sku=209222868


is that a good deal?