Have you looked into ting? (ting.com) They currently only have android, and they are just using Sprint's network but they are month to month and it is super easy to turn off data.
After a 2-3 month trial, I've switched everything to Ting (and bought stock in Tucows). Ting's rate plan and philosophy, or something similar, is the future. Just so long as Sprint doesn't kill them off....