I was checking out the yoga ball for rolling the upper arm/scap area from the beast skills blog http://www.youtube.com/watch?v=dxY8fqgzeZc
I found a perfect subsitute to the 20$ ball in my sons toy box. The sky ball 7.99 http://www.shopgadgetsandgizmos.com/product/18521/
I think you can get them at most toy stores too. And they bounce 75' high.
I foam roll every day and this ball found spots around my shoulder blades that made me want to cry.