You might wish to look into a MiFi plan offered by Clear (which was recently subsumed by Sprint).
You'll need one of their MiFi devices, and their plan is about $50.00/month.
It is REALLY unlimited.
I've used it from Bangor, ME to Seattle, WA, Minneapolis, MN to Brownsville, TX and all points in between.
It is never throttled back, and performs well, so much so that the MiFi device can support up to eight other devices (tablet, laptop, phablet, smartphone, etc...)
This is a link to their website:
http://www.clear.com/
It is the best $50/month that I spend.
They have two plans, one for $40/month, one for $55/month.
You aren't tied into any contract, and you can use it for three months, turn it off, and turn it back on for four months.
Its truly a pay as you plan.