On a long-ago thread, I listed out the read and write speeds of a ton of different 2gb SD cards. Sandisk Ultra 2s were strictly "middle of the pack", actually slower, than most cheaper cards. They read and write at 10m/s, which most cheaper hi-speed 133x/150x cards write at more like 13-15m/s, and read at 22-23m/s (off the top of my head.) One of these days I'll redo that list and put it on my site, so I can find it again.
Basically, you're paying a lot for the Sandisk name. If that makes you feel good because you trust their quality, that's fine - many people feel that way. I'm not willing to. Much of the time, I use an Ultra (that's the brand, not Sandisk) 133x 2gb that I got for $20 after rebate from ZipZoomFly, and I also have a PQI 2g 150x 2gb that was something like $25 after rebate.
FWIW, there is also the Sandisk Ultra 3, which does have faster write speeds than most cheap 133x/150x cards - but I think it's over $100 for the 2gb card, and it's virtually impossible to find.
Generally, most 2gb cards are pretty fast and you shouldn't notice a difference. The other day, I took just my camera (no bag) to my parent's house to take a picture of a train table I've been building for my son, and didn't realize that I had left my usual card in my computer. Oops! My father came up with a 16 meg card to borrow - enough for exactly
one photo in RAW mode

- and man! Did it take a long time to write! The difference was very clear. But I doubt you'll find a 2gb card that slow...