Any of those knock off hot boxes/ easy vapes on ebAy. But honestly one of the worst I think is the atmos raw ( to be forthright I have never used one but I have never heard a positive review from someone with other vapes to compare to)
I made one out of a 40oz bottle, a soldering iron & a metal bowl when I was in college. I was trying to find a picture of one to post when I stumbled on this gem. http://www.build-your-own-vaporizer.com/index.html