Wow, I didn't realize how Ting actually worked. I thought it was a thing where you basically get to choose your plan, mixing and matching different tiers of voice, text, and data usage, but they actually automatically bump you up or down tiers based on your ACTUAL usage.
So it's essentially like prepaid, in that you pay for whatever you use, but instead of true pay-per-use, there are breakpoints above which you pay extra. The rates are really good though - if you strictly limit your data and don't go too nuts on talking or texting, you would probably pay under $30 a month.
Ting uses the Sprint network, so that's something to keep in mind. They don't have the best coverage everywhere.
I was going to point out Platinumtel, which has true pay-per-use on everything, with pretty good rates. It's 5 cents per minute, 2 cents per text message, and 10 cents per MB of data. Again, if you watch your data like a hawk or just disable it altogether you could have really low bills. And you don't have to worry about paying for minutes you don't use or incurring overage charges.
It uses T-Mobile so again there are some network concerns, although it appears that they do offer voice roaming on AT&T towers THIS IS ACTUALLY NOT TRUE, I WAS MISTAKEN (important for me since I travel across Wisconsin every few months and there are no T-Mobile towers anywhere between Eau Claire and Green Bay).
One nice thing about T-Mobile is the data is actually fast, unlike Sprint. But it sounds like, for your use, data is not a concern.
Also, both Ting and Platinumtel offer Bring Your Own Device - Ting lets you bring over any Sprint device (other than iPhones and Windows phones), while Platinumtel will let you bring any GSM device, just pop in a sim card.