J.B.
We had both our teens on Straight Talk (Walmart) for a couple of years before switching to a phone with a plan.
The signal on the pre-paid phones is great because they use the towers from all the top carriers. The billing is done monthly charged to a credit/bank card or you can go once a month and refill it. We just had a bank card tied to it, made it easier.
There weren't any hidden fees, taxes are what they are. But the Straight Talk phones ran around $35 a month with unlimited talk and text.
Tracfone works the same. You can even get iPhones on the month to month plans now.