I looked into it, as I didn't like the pricing of what you could buy, and it doesn't really end up saving you that much. For it to be a true "misting" system, the pressure needs to be somewhat up there(I forget the specifics).
Its not hard to find a pump that will provide the required pressure, but you end up finding a trade-off between price and size. You can get some decently cheap water pumps, but they're designed for sprinkler systems, where you aren't too concerned with the size. They also will not be designed for the macroline rubber tubing used with most misting systems.
Long story short, you'll only save about 25-30 bucks, to have a hacked together, unwieldy, long-term project on your hands, and unless you're a plumber(or any other profession dealing with fluids under pressure) you will most likely have tons of leaks. The time saved, and ease of setup is worth more than the money saved in my opinion.