I was looking for a cheap phone for my son, and ran across this deal.
Samsung Galaxy S4 - $14.99
The site won't let me check out without a plan, so I got the minimum $20. The plans are non-recurring (i.e. you don't have to cancel). If you want to make it recurring, you can update your account via their website.
I did a little research on enTouch and found out they use the Verizon network.