I am still using the bottle that came with it, may be small but does go for some time, mind you I've only used it a few times at conventions, jetpack is a little heavy to lug around all day. I have read reviews on the site and quite a few say it lasts a long time.
I was going to try mixing some myself, on the Microfogger site it says it uses 2 chemicals, Propylene Glycol and Vegetable Glycerine, I guess it would just be a matter of playing with the mix.