Just for reference, this is how much it costs you to use up a megabyte of data in various mediums:

text message: $327.68 
kindle book: $11.10 
pay as you go data usage: $3.00 
average iphone app: $2.71 
itune song: $0.33 
average cell phone overage minutes: $0.11 
average steam game: $0.03