I get all my Kona cotton solids at Hancock's of Paducah. I get black by the bolt and other colors in 10 yard cuts (think I have about 20 colors plus PFD right now). It goes for $3.98 a yard at Hancock's of Paducah.
As for the claim that the Kona solids at JoAnn's are of a lesser quality, that issue has been addressed before and Kaufman Fabrics replied "in person" here:
http://www.quiltingboard.com/t-33854-3.htm#746926