T-Mobile offers its Simple Starter Data Plan, which includes unlimited talk and text and up to 500MB of 4G LTE data for $40 per month. It has no data overage fees. (You won't be allowed to go over the 500MB limit, unless you choose to pay for extra data.)

Of note, T-Mobile also offers its Simple Starter Data Plan with unlimited talk and text and up to 2GB of 4G LTE data for $45 per month. As above, there are no data overage fees.