Regardless of what the official rate is, or may be, I would figure on paying about $30 one way for two people, plus $1 per bag, plus tip. (Plus extra if you are making a stop at a grocery store or to pick up some beers, etc). That will get you pretty close.. Plus about 50% more if it's after 10 PM.

SXM really isn't the kind of place where you can complain to anyone about someone exceeding the 'official rate'. And actually, since Orient in on the french side, not sure they could control how much someone could charge to go to the french side anyway. But regardless, above amount should get you close enough.