Ok, heres a few I know of off the top of my head
Mexican dwarf boas-Not a common as some of the others but they are only going around $300 for adults
Hogg islands-Lots available, males 5' tops and females over 6' are big. $100-300 depending on overall quality. Some adults are going for over $300.
Central American-6' is an adult size with the ocasional 7' I'm sure being out there. I believe these are known to be more nippy than some of the others.
look at www.riobravoreptiles.com and see what he has about the island localities. Gus knows locaity boas better than most