Cheapest att phone available that will work (battery life is crucial)?

[Runwithme1]

I have an att sim card, and basically I'm hoping to find a very cheap working phone, used or new, which has pretty good battery life. I would like my phone to last at least an entire day with only 3 or so hours talking. I'm a college student on a fixed income, so although I have some money, I really don't want to spend any more than I have to for the features I use in a cellular phone.