Millenicom will give you 20G/month for about $69/month. I just got their 3G/4G Mifi and recommend getting a Wilson Cradle to boost the signal for cross country driving. You buy the Mifi from Millenicom. The 3G store is the place to go for the Wilson Cradle.
Last October we were in Montana for a month from Glacier Park to Custer's battle field and in the last two plus months we've been in some remote places and were able to get internet or at least a better cell phone signal when we needed it.
The Wilson cradle amplifies the signal for our cell phone as well as the Mifi. It's really easy to use.