The Enchantment will have a drink station (usually near the pool) that offers coffee, tea, orange juice and the like in the morning and then switches to coffee, tea, lemonade, punch and such for the balance of the day. There is no charge for the beverages and it is a self-serve station so you can get all you want.
They will also offer free ice cream in the afternoon near the same station. There is also beverage stations in the Windjammer Cafe that are open most hours. One good buy if you drink sodas is to acquire an all-you-can-drink soda card at the begining of the cruise. I think they are around $25 or so. This will get you free cokes and such 24 hours a day.
If someone wanted to, they could go on a cruise and not spend a cent (other than gratuities)
Read the port reviews for both Ocho Rios and Grand Cayman to see what there is to do without spending a bundle. www.PortReviews.com
You guys will have a great time.