I suppose you could look at it as a fee, but it comes down to how much the Cambio owners feel that the dollar exchange is worth.
Yesterday the Cambio downtown in Coral Seas Plaza (Gold Nugget) was 121 to 1 and Banmark, past the Texaco was 121.5 to 1.
This past summer when the J$ was in freefall, the interbank rate was 138 to 1, the Gold Nugget was 125 to 1 while Banmark was 127.5.
At that time there was a higher risk for the Cambios, so the rates were much lower than the interbank rate.
Essentially capitalism, supply, demand and the exchange rate risk involved determine the rate.
Rambo asked about "the street rate" which is determined more on the fly. You may be offered 110 to 1 because a non-dollar trader doesn't have all the resources that a cambio or bank has at their disposal. With the dollar hitting 138 to 1 just a few months ago, the small businesses can't absorb the risk as readily as the larger traders.