after doing some math i just decided to leave mine on the cheap plan all year. i take it with me somewhere nearly every month and of course during seasonal trips it gets used a lot.
i cant justify changing plans for the few times i get charged a dollar or three extra.
This is what I have done for the past two years. Highest bill I have had was $20 or so. I take it on car trips where I loose service and it is nice to just grab it and know it has paid service.
My three free presets are set to cover about 80% of my communication needs.