So obviously I've got my one ball python and I had a leuci Texas rat for two months, but then he escaped and we're preeeetty sure he either froze, dehydrated, or was discovered by the dog. I've got an 18x12x12 ExoTerra glass tank that I'm going to try and trade it to my biotech teacher for a generic 20 or 30 gal. Now I have to find something to put in it.

The obvious choice is another bp. The only thing is if I get another, I only want a female pastel, and without a job and going into college, dishing out $200+ isn't easy.
One of my other top choices is a pair of corns. I'd like to try them as a first breeding project if I can't do the pythons. I've heard they can be housed together, even as adults, but does this hold true for 20-30 gals? I'm also a bit more wary about high-energy colubrids now that the rat snake escaped and got out of my bedroom so fast. I think I'm still more comfortable with slower pythons and boas.
I also really, REALLY like Tarahumara mountain boas, but I'm pretty sure they won't stay in a tank that small for very long, they're probably far out of my price range, and they're hardly ever for sale. Buuut it's also almost impossible to find a care sheet for dwarf boas specifically, so I don't know for sure.
I'd also like to avoid things like Kenyan sand boas, rosy boas, milksnakes, Cali kings...the generics. Also primarily arboreal snakes like GTPs and ETBs are just not for me, at least for the time being.

So, any suggestions? Also, sorry if this is in the wrong place. ^_^;