Its true that they are cheaper but those aren't shields. Those are development boards for the codec. Kind of like how the arduino is a development board for the atmega328p
seeedstudio has one based on the same chip
but it is 27.50
http://www.seeedstudio.com/depot/music-shield-p-642.html?cPath=132_134
Meh, I've already deconstructed sparkfuns mp3 shield.
I'll just make my own.