Previous posts outlined costs pretty well, but I'd be careful getting the really cheap ones. Imported snakes often go for less than half price of a CB snake, but have tons of problems. It's best to invest. Usually the $250 to $300 range offers snakes that have poor color or pattern and no locality info. Reputable breeders seek to enhance these conditions and that's where it pays to shop around. There are several different localities and some can be quite different and/or have variations in prices. You can get a nice s.e. Chinese or Sichuan mandarina for as low as $400, but I'd be careful who I was dealing with.
There are many breeders of mandarina that visit this forum. Not all are businesses either. Some, like me, are just hobbyists, and may only have one pair of these snakes. But there are times when they have babies they'd be willing to part with. I have one left from this year's clutch, but won't be selling it. I'll keep it until next summer at least. I also picked up a pair of Sichuan mandarina from a friend this summer. They are an awesome color/pattern phase and, so far, seem like a somewhat different snake in behavior and morphology. They are supposed to get larger than the more common forms too. If you go this route be careful to get a reputable dealer who knows exactly what he's got.
Good luck in your search. Mandarina is one of the most awesome of all the Asian ratsnakes.
TC