#Royal Caribbean International
Royal Caribbean is one of the largest lines, setting sail hundreds of times each year to destinations around the world. And having the ability to accommodate thousands of guests per ship allows Royal Caribbean to keep rates low: Cruisers won't have trouble finding itineraries costing less than $150 per person per night. Prices cover lodging, meals in the Main Dining Room and a wealth of onboard activities ranging from swimming and rock climbing to Broadway-style performances.Carnival Cruise Lines
Carnival Cruise Lines specializes in low-cost fun, offering frequent sales and early booking rates on already low prices. In fact, finding an itinerary for less than $100 per person per night is the norm for passengers on Carnival's 24 ships. Although the line's rates don't cover some necessities (like beverages), cruisers can choose from a variety of drink packages tailored to a wide range of preferences and budgets. As for access to the ships' pools, water parks, mini-golf courses and evening entertainment — well, that won't cost you a penny more than your standard fare.Celebrity Cruises
Albeit smaller than some competitors, Celebrity Cruises has an advantage over other affordable cruise companies: diversity. Celebrity only has 10 ships, yet it offers the floating-city experience of a larger ship as well as the intimacy of a smaller boat. And you can't argue with the rates: Cruisers can find Celebrity itineraries costing less than 0 per person per night. The line also shakes up the dining standards, allowing guests their pick of specialty dining venues for one flat package rate; meals at the main restaurant are covered in the cruise fare.Norwegian Cruise Line
Norwegian is quickly becoming a force to be reckoned with in the cruise world, expanding its fleet and offering affordable trips to destinations around the world. What's more, Norwegian doesn't charge extra to ditch the steadfast cruise rules — such as dress codes and assigned meal times — still enforced by other lines. Those who travel with Norwegian can eat whenever they want, wherever they want, wearing (pretty much) anything they want. And though meals at specialty restaurants will cost extra, several eateries across the fleet offer dining for as low as $20 per person.Princess Cruises
You can expect to pay more for a Princess Cruise than you would with Carnival (the line's parent company), but not much more. And while Carnival tends to cater more to families, Princess' 18 ships were designed with adult travelers in mind. On top of lodging and dining, fares cover enrichment programs, such as cooking lessons, photography workshops and art history lectures, as well as a variety of fitness classes. Meanwhile, Princess' "cruisetours" (optional extended stays in a port of call) allow you to experience different destinations for less than what you'd spend on a traditional land-based vacation.
#Holland America Line
Whether you opt for one of Holland America's kid-friendly ships or an adult-oriented boat, you'll find cruising with this line to be a pretty good bargain. In fact, you can find seven-day trips to destinations in Caribbean for less than $100 per person per day. But on this line, cutting costs doesn't mean skimping on service. Since each ship houses one staff member per every two guests, Holland America offers more personalized service than many of its mainstream competitors.Costa Cruises
Also a member of the Carnival family, Costa Cruises is primarily based in Europe, though the company does offer voyages throughout the Western Hemisphere. Still recovering from heavy scrutiny after the Costa Concordia accident in 2012, this fleet continues to offer rates that are considerably lower than usual. Although there are family-friendly amenities, Costa is better suited for adults and offers dance and language classes, a library and evening theater productions, all of which are included in the cruise fare.MSC Cruises
MSC caters primarily to European cruisers, but the line's rates don't come close to matching those of the typical European land vacation. Once you get past the cost of flying to a foreign port of call, MSC will allow you to experience destinations around the world at extremely reasonable rates, with cruises around the Mediterranean, northern Africa and South America costing less than $100 a night. In addition to dining in many of the onboard restaurants and access to facilities like pools, cinemas and bowling alleys, MSC rates also cover fitness classes and gratuities.