if your willing to put a bit of money into it animal plastics look good and work well for keeping humidity (i havnt got my snake yet but im relaying information that ive got from threads i started myself ) and as for expasion you can get dividers for them as well, so you could buy a larger one even for a baby then take the dividers out as he/she grows

worth checking: http://www.apcages.com/home/

you can click on terrestrial cages on the left, im planning on getting a t8, after you click on t8 (ive heard t3 works too?) and then onthe far right they have a plastic divider addition for an additional 20$

again this is relayed information from other users that i trust, but its all good stuff