Assuming that you need prepaid and you need a cost effective solution you best bet would be T-Mobile, you need to check their prepaid coverage in your destination city. Prepaid plans usually have roaming charges but only for voice and sms. Check the following link -
http://prepaid-phones.t-mobile.com/
Assuming that you are having your phone from your own country then you need to get a SIM card in USA which you can buy at some superstore say walmart where you can see multiple options as per your need.
