Hi, there are a few dwarf boas. Some are lower priced than others. I acutally just purchased a pair of Sabogae "Pearl Island" boas, which only reach around five feet. They also do not grow as thick as BCIs or BCCs. Sabogaes are still a little on the expensive side, at least for ones that have paperwork. Here is a site that has a lot of great info on dwarf boas: http://cuttingedgeherp.com/ , and here is another http://www.riobravoreptiles.com/ .
Good luck.