The coupons are here
on Carnival's site.
They have the price at $21.25 and are inclusive of gratuity and (Delivery Fees).
I was trying to do the math and did not see the Delivery Fees. I could not get it to balance before I saw this. Unless they have raised the drink prices during the last few weeks, I think the Bar Credit Coupons cost more than buying a drink on board.