I biult one for about $50-60... and am about to begine making a bigger and better one. My new one will have a better airflow etc.
Here are some notes on my simple cheep one...
http://www.naplak.com/modeling/tips/painting_hood.htm
www.naplak.com/modeling ... a free site for modelers
www.scalehobby.com/forum/index.php ... a nice Modeling Forum