I'd buy the smallest one and then one of those Wireless Seagate iPad HDDs they've got out now. You can get much more space for the money than you'll get from Apple.
Apple markup is nuts. I paid $25 the other day for 2x4gb RAM for my MBP. On the Apple site they wanted $400.
$200 get's you 500 GB of Wireless iPad Storage.
http://www.amazon.com/Seagate-Satell...2141344&sr=8-1