So, while at Petsmart picking up food for the cat, I stumbled into the "dog toy" section and found some nice, light balls for 99 cents each. They were 3 inch balls. I bought one to test. Brought it home and cut it open a little less than half way, and squeezed a beanbag inside. A little superglue and wait for it to set and you have a stage ball. (Well, I guess it's more like an MMX Ball (http://www.inthespinjuggling.com/t_store/balls.htm)
Issues: The balls are *soft*, so the hardest part was actually lining up the seam to reglue the ball together. I had to reset and reglue the ball twice before I got it nicely line up. One of the balls was a little flat on one side, but that hasn't really thrown off the balance to my notice.
Speaking of balance, if you shake the ball, you can feel the beanbag move around inside, but there's almost none of that when juggling.
The balls end up being heavier than a standard stage ball. My arms certainly feel it after five ball runs.
The issues are minor, in my opinion. Better to give these loyal bags new life :)