To be fair, they were selling service so low it really was cheaper than it should have been. It was only a matter of time before a rate hike of some sort would happen.
It seems as if T-Mobile USA is following the lead of other major US carriers in that they only want to directly sell to power users. Customers who aren't as profitable are being steered to their own discount brand (MetroPCS is owned by T-Mobile; likewise, Boost and Virgin Mobile are owned by Sprint while Cingular is owned by AT&T) or third party MVNO resellers like Page Plus, Straight Talk, Pure Talk, Ting, and the like.
If you want to continue to use the T-Mobile network but with a cheaper plan, there are plenty of ways to do it.