Thats just a regular Cagle's map turtle (Graptemys caglei). Its no special morph or anything; don't buy in to the scams that those dealers offer. I wouldn't recommend a map turtle as a first pet either, but if you decide on a map, I would get something cheaper such as a Mississippi map or false map (Graptemys kohni and G. pseudogeographic). They usually aren't more than $15.
~Mike