Why even bother with trying to get a plan, just pick up a GoPhone sim on ebay. Prepaid data is $19.99 for 100mb...kinda pricey, but if you're using an iPhone you're kinda locked into AT&T for the best experience. EDGE on T-mo is noticeably slower, maps take forever to load. You are just not going to find a "decent data cap" on prepaid.
True but I am unsure how much data that I would need. I plan to use Google Maps a fair bit and using it for Facebook and Email. I guess that I could test it on my phone before I go to gleam some info as to my data needs but dam the data sucks ... lol.