SD cards are on sale at Amazon today. You can get a 32 GB card for only ten dollars right now. You can actually get even bigger cards, like a 128GB SDXC card for 49 dollars. We don’t recommend actually picking that one up though.
You see SD cards are most commonly used for the 3DS in the gaming world, and it might be a good time to pick one up considering the New Nintendo 3DS is coming out soon. But Nintendo only officially supports SDHC cards, not SDXC cards. Higher space cards should be OK as long as you format them to FAT32, but just in case you might want to keep your purchase to 32 GB, the highest SDHC has to offer.
Source: Amazon