that is actually a great deal! in most canadian stores that sell them they go for around $1000 CAN! I geuss it also depends if the snake is healthy, or if they're having problems feeding him,etc... but if none of that, it could be that he/she isn't considered a "pretty one". If it's none of that , it could be because he is unfreindly, they do have very large teeth and most dont like beaing handled. My uncle has an emerald tree boa that surprisingly likes to be handled and when you are done he doesn't like to go into his cage!
good luck, Lucas