Dwarf burms are hard to find and I hear a lot of fakes are being passed off. I also hear they are mean as heck and never calm down. Last year, the few I saw for sale were thousands of dollars..
True super dwarf retics however, are much better to have, only cost about $200 or so depending on breeder, and have great temperaments.
There are only a few people actually breeding the true SD's so they are not available very often. Many people are just using them to breed down the size of mainlands and get smaller color morphs but then they are not true SD and will get about as big as a dwarf and not an SD.
Check kingsnake.com I've seen some there recently.