I got a "Virgin Mobile" phone for $20 (there are cheaper models). I bought it from their website, but they are available in LOTS of places (Radio Shack, KMart, Rite Aid, etc).
You use your CC to dump money into your account..........two cents/minute......less if you buy them in chunks.
I don't use a phone often, so my monthly bill will be less than $10.
They offer all types of plans if you use a lot of minutes or need texting, etc.
http://www.virginmobileusa.com/