What is the cheapest iPhone 5 plan available right now?

I want to buy an iPhone 5 this summer. I'm working the entire summer--minus a few weeks where I'll be at camp, vacation, etc. Buying the actual phone is no problem, but it's the monthly bills that I need to do research on. My mom is EXTREMELY cheap, and I want to have a good solid cell phone plan when I ask her if she'll pay the monthly bills. What's the cheapest plan available right now? What carrier it is doesn't matter, but Verizon is preferable. If there's something cheaper, though, it doesn't matter what carrier.
Also, are there cheaper plans for the iPhone 4s? I'm willing to buy the 4s if it's even cheaper than the 5 plans.


Virgin Mobile - they have unlimted data and no contracts