i just did about 3 hrs of research on this. if you made one yourself its gonna cost you about the same as if you just bought yourself a misting kit/humidifier. you can get a cheap humidifier from walmart for $40 of so but its gonna be nearly 100% manual and you need to plumb it into your tank. personally, it seemed best to spend around $100 as don said on the monsoon or competitor. there is a thread of a review of this item compared to the fairly new mistking kit. try to search for it, its full of good information. personally, this is what i recommend:

MistKing Misting Systems by Jungle Hobbies Ltd