I've been given a lot of conflicting information, i.e., you are suppose to tip this odd assortment of people every day; a can of Coke can cost up to $2.50 each; if you eat a meal that is not your specific dining assigning it can be as much as $50 per person per meal; anything served to you outside the dining room is an extra charge; just to get off the ship at any stop, even if not taking a "tour," you pay an additional charge; etc., etc., etc.
You certainly have been getting alot of MISINFORMATION.
There are unfortunately no standards which will apply to every cruise line. However there are some general items which do.
There's never an extra charge to leave a ship in a port of call, unless you're heading to countries which require visas (like Turkey for example), where you'd have to purchase a visa. In the Caribbean, no visas are required.... so no extra costs.
In some port stops, the pier is a fair distance from any beaches or attractions, so even without doing tours you'd need to budget some money for taxis or buses.
Other than some ships "alternate restaurants", which may have an extra service charge, every ship has dining rooms and buffets where you can enjoy EVERY meal throughout the cruise at no extra cost. The vast majority of ships also offer 24 hr room service at no additional cost.
If you don't consume alcohol, don't gamble, don't use spa services, don't do tours, don't shop, and can be satisfied with non bottled water, iced tea, coffee, and juice ... rather than sodas, and eat in the cost included restaurants... you can go on a cruise with very little added expense over the cost of the cruise ticket, and $10 per day for each of you for tips.
So.. for example on a 7 day cruise.. your cruise fare PLUS $70 per person.
That said, it's probably not realistic that you aren't going to do ANY of the things listed above. So the question really becomes HOW MUCH of the extra cost items you chose to indulge in, and to budget for those.
in the cost : all meals (avoiding the surcharge restaurant (or restaurants depending on the ship), all entertainment (showrooms, and lounges), poolside games and activities.
There are NO shore side activities included in the cruise fare.
Hope that helps. Any more specific questions, feel free to ask.