Try Page Plus Cellular.
https://www.pagepluscellular.com/
They use Verizon Towers and your phones will work with them. They have unlimited plans available....but if you are willing to set your phone to use Wifi only, the $30/month plan gives you like 500MB of data a month. A coworker of mine does this and loves it....
The only con to all the pros of switching to them is they don't own the towers, so they only get 3G service. If you've got an iPhone4, that will be perfect for you.
StraightTalk is the other Verizon-tower service....they have far worse customer service and I've been instructed to stay away from them...they grew too big, too fast and still haven't adjusted.