This is crap journalism at its finest. 1MB of SMS messages is about 6,500 texts (assuming that all of the 1MB is SMS, ignore overhead for this conversation). 6,500 texts would be more appropriately classified in the Unlimited $30/mo plan.
So, 1MB of SMS costs $30/mo on AT&T. Unless it's a slow news day and we extrapolate from the worst-case scenario.
Most people who are of a legal age to sign a cellphone contract generally understand that pay-per-use scenarios like this are rarely the best way to go.