16 x ($6-10) = $96-160.
Depends on what you drink. A bucket of beer is probably your cheapest bet.
--They serve them like normal. There are multiple bars on board where you can simply walk up and order a drink, there are tiki bars by the pools where you can go up and order, their are cocktail waiters/waitresses who will bring you drinks where you are sitting/laying out, and your waiter/waitress will bring you your drinks at dinner, and there are people that will bring you drinks in your stateroom too.
EDIT: I found this link, should be helpful to you
http://cruises.lovetoknow.com/wiki/How_Much_Are_Drinks_on_Carnival_Cruises