You Get What You Pay For
In my experience there is a definite difference between cotton solids from Joann's Fabrics (Kona or not) and Moda or Kauffman Kona solids.
The cotton fabric from Joann's has a looser weave, is much more apt to bleed, and has a considerable amount of "coating" or sizing on it - very stiff even after washing.
The slightly higher price for quality cotton solids is worth it to me, especially when hand piecing.