I used the handy dandy packaging the ping pong balls came with to paint them.
Even the paint I use is free. My local trash dump recycles paint and other household chemicals, which are still viable. You can go to a special section and pick what you want for free! So, I used my free white spray paint on my yard sale ping pong balls.
I cut out some numbers and used scotch tape to steady them. Then just rubbed the numbers on. I did run into a glitch...the numbers cracked do to the roundness of the balls. I started to use a sharpie to fill in the cracks with great success. But then I decided that I like the shabby look of the cracks and liked also that it was the lazier way to go, which is very appealing right there.
So I left 'em as is and I really like that they only cost 25 cents and helped the land fills.
Ping Pong anyone?