I agree that the above prices are way too low. A friend and I were talking about this just yesterday. I just finished a 55 x 70 quilt. In fabric, alone, I'd spent $70. If you had it quilted (at an LQS) on a long-arm machine, it would've cost $90 to quilt with an edge-to-edge meandering design, and to bind it. So, factor in my labor (say, 8 hours to piece it, total). That's another $50 - $80, depending on the complexity of the block.
Bottom line, at twin size quilt would cost $210 - $240 in material and labor at base price.