US prepaid plans

My sister will study in New York City for a total of 12 months starting January 2014, with several 2-month-breaks. This is why she needs some kind of prepaid plan for her phone, so she’s able to choose if she wants to make use of her phone at the beginning of each month. She will be getting a Moto G (she doesn’t need LTE) for full price as it’s pretty low, and we’re looking for something like 1GB of data and maybe 100 free SMS/calling minutes included for less than 30€/month. I’m german, and I’m having troubles getting the US carrier situation regarding prepaid. If there’s such a plan or a similar one, can you help me out?