"Low minutes"? T-Mo has two $30 prepaid plans:
- 100 minutes, unlimited SMS, 5 GB of 4G data, unlimited 2G data
- 1500 minutes or messages, 30 MB of data
You either get few minutes or few data, not both.
Anyway, I believe overage fees are 10 cents per minute, which means 100 more minutes for $10. That's reasonable. In fact, I would rather get a low minute allotment and be charged a reasonable amount for going over; this means I won't pay for minutes I don't use.