I guess I'm just a fan of smaller things, might be because I come from NYC apartment life lol.
i call bull on this one, i have been to NYC many times and your cockroaches are bigger than my dog!!LOL
seriously though, if you are looking for a cheap animal that will utilize the height, either grey or green tree frogs are the way to go. $6-$7 each. you can feed them small crickets, also cheap and readily available. another choice for frogs would be white's tree frogs. a little more expensive $20/animal, and will live in a group without a problem. that sized tank, i would put no more than 3 in it. they are easy to care for and have great personalities.
as far as reptiles go though, i have no clue. i'm a frog guy, if you couldn't tell....LOL oh, and if price is a consideration, forget any dart frogs, they START at about $30-40/animal. good luck and keep us updated!!