I've looked into asian green vine and I do think they stay pretty small, but I thought they needed super high humidity, like 80%+. I'm not sure I could offer that, but maybe I could.

There a varaity of types of beauty snakes. Taiwan, vietnamese, blue, etc. Wikipedia says these are different subspecies. Each subspecies might average at different lengths, but I don't know which ones are usually shorter. Every pet store calls them something different as well, so I wouldn't want to take the gamble and hope that I'm getting a shorter one. The people at the Serpentarium breed them and they sell them, so I could get one easily, but it was theirs that were up to 9 feet. Here's a link about the snake in general.
http://www.bluegorgon.com/caresheet.htm