I was on the Sun last week. There is no "surcharge" unless you are referring to the $10 cokage fee for wine. In some ports of call, the shops automatically sent your liquor to the ship, in other ports they didn't. In Cozumel, I walked on with a bottle of Tequila, through the xray machines, and no one said anything to me.n When we were in St. Maarten same thing, some people had their bottles boxed up and it was easily detected, we put ours in a bag and walked on the shop with it. (We had a bottle of rum, and 2 bottles of wine.)
You can get alcohol at the duty free shops on the ship and it is comparable to what you can get on the islands.