⑻вιт☆ʂɐɱʊяαɪ, making sure you properly read the original post, you don't generally buy the premixed PAX. You just buy the prosaide adhesive online, and buy the paint at your local craft store.
Fxwarehouse prices tend to be quite competitive. And you pretty much can't avoid having to pay shipping; it's a specialty item. Still, doing the math, it just doesn't seem that costly to me.
4oz Prosaid + shipping + 4oz Liquitex Basics paint = about $20, or $2.50 an ounce.
2oz Prosaid + shipping + 4oz paint = about $15, or about $3.75 an ounce. (plus leftover paint for drawing a pretty picture!)