Hi,
I have purchased a Motorola C168i (
http://www.motorola.com/Consumers/US...168i-USA-US-EN) for 20 dollars from Wal-Mart and I love it - sturdy, easy to use and battery lasts forever. The plan is AT&T Pay as you Go, which per day costs 3 dollars for unlimited calls (or) 1 dollar flat + 10c per minute (or) no flat fee + 25c per minute.
And because every 100 dollar top-up is good for a full year, I just keep it as second phone for whenever I travel to the US (if this applies to you)
Cheers,
J-