Cruise prices fluctuate wildly based on the time of year, the destination, and what type of room you're booking. But it's possible to find rooms for less than $100 per day per person. If you're living on a cruise ship full-time, $3,000 per month can seem expensive. Keep in mind, though, that you'll also be saving money in other areas. For example, most food and drinks are included in your cruise fare. So unless you're splurging on specialty drinks or fancy restaurants, you won't need to budget much for food. You also won't need to worry about other costs you're...