I have an empty 40g tank. I'm trying to think of something to put in it. I really want a lizard or a snake other than a ball, corn, or red tail boa. (My red tail will probably go into it when she gets big enough, but until then, I can house something else in it. So if you had an empty 40g, what would you put in it?

1) It has to be able to live in the 40g tank into adult hood.

2) It has to be relatively inexpensive to keep (feeding wise. Heat is no problem)

I probably won't put anything in it for a while since we are moving, but I just wanted to get some ideas.