Mini pcie 3g - 4g card for linux remote monitoring

I am building a standalone remote ubuntu 14.04 server that will not be allowed on an internal network. I need to have some way to ssh onto it. The motherboard has a sim card holder and mini pcie slot for a 3g/4g modem card. Any suggestions on which card to get and also a low cost sim card service provider? I only expect to use a few Megs of data a month. I don't really want to pay $30 per month, maybe $10 tops if possible.