I've looked at this from all sorts of angles and think you will have a hard time beating the price and quality of the misting sytems from Marty at mistking.com with a DIY system with a powered pump. For all the chasing parts, fittings, etc., you will have a hard time finding a pump that really produces quality mist for less.
The only exception I can think of is using a espresso machine pump such as the Ulka pumps, but I haven't heard much about anybody trying that. If I find an espresso machine at Goodwill I may try it someday. From what I understand the trick is that they use vibrating pumps instead of the vane pumps.
Some folks use a hand pump canister to pressurize the container that powers the misting system if you don't mind a manual solution.
Marcos