Nah, it's not THAT expensive! And I have to believe that it would be worth the money to save yourself the absolute mess of trying to make it yourself; I mean, this stuff is messy by itself--I couldn't even imagine trying to make it yourself!
Besides, I'm sure they have some "secret ingredient" that makes it so easy to work with; and I doubt you're gona find the formula on the internet--it's probably like the modeling equivalent of "Classic Coke"!