Depends on what price the local breeder is going to sell them to you for. If the price is right you can co2 and freeze them yourself. $13 for those rats is insanity. If your snakes are feeding on F/T and you only have two snakes I would highly recommend buying F/T in bulk (online or at a local show). With only two snakes breeding rats is really not worth the hassle and $$
http://www.metalmonkeyexotics.com/blog/?page_id=331