I am using a Sprint Mifi to do exactly what you are wanting to do. Someone told me about The Calyx Institute
https://www.calyxinstitute.org which provides unlimited data to it's members. The first year is $400 and that includes the Mifi device. That is $33 a month for unlimited data. The second year I think is $300 which is $25 a month. Not bad for unlimited data. It's not supper fast but we have a Roku TV and it works fine. As long as you have a decent Sprint signal where you at then you should be good. We have been doing this for about a year and we are very pleased with how it works.