If you donlt find one and you live in an area served by RiteAid or CVS (they both sprout up like weeds on the empty corners of busy intersections around where I live), and I'll guess Walgreens, then go there and look for a Nokia pre-paid T-Mobile phone for $19.99.
That's about the lowest price you'll find new/off the shelf T-Mobile pre-paid. I saw these in two different RiteAids in the last few weeks. They usually have one or two at a time in stock.