It's probably a lot less expensive, even allowing for the taxi to Marigot, to go from there, but I far prefer the airport service myself at whatever the cost. We usually do GB Express and appreciate their service but they are definitely much more expensive.

Not certain, but I don't tecall anyplace close to the Dutchside ferry dock to buy sunscreen but I know you could easily get it in Marigot or along the way. Safe travels.....