Woman holding her boarding passes

When it comes to booking a cruise, people generally gravitate toward travel agents, popular online booking sites like Expedia and Orbitz or go directly through the cruise line. They're familiar and easy. But there are a number of lesser-known places to book a cruise -- which open doors to attractive price tags and unique extras. Some might be places you already shop, but never thought sold cruises.

In most cases, fares from these alternative sellers are competitive and roughly the same as what you can find online. The true bargain is what's included in the offer. (Double airline miles, anyone?) If you want to broaden your search options and potentially get more "bang for your buck," here are seven unusual places to book a cruise.

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1. Wholesale Clubs

Members of wholesale clubs like BJ's and Costco receive exclusive rewards when they book cruises through the companies' travel arms. BJ's, for example, offers up to $500 in store credit ($25 for repeat customers) for booking. Perks Rewards Members also receive $50 onboard credit. At Costco, Executive Members have access to extras like room upgrades, onboard credit and spa credit. If you're a frequent wholesale club shopper, it's a win. Snag that $500 gift card, and your cruise pretty much covers your next big shopping spree.

2. Airlines

Spend a lot of time in the air? You can book a cruise through your airline, and earn miles for the transaction. Major carriers such as American Airlines, United and Delta award members up to a certain number of miles for every dollar spent when you book a cruise. The amount of earnable miles also can increase, depending on the cruise line, cabin category, when you travel and other factors. Additionally, airlines offer exclusive deals and other perks, such as cabin upgrades and onboard credit, to people who book cruises with them. Frequent flyers can use their airline miles to book a future flight, hotel stay or even another cruise. Cruises are priced in miles and vary based on itinerary, length of cruise, cabin category and more. For example, a three-night Bahamas cruise on Carnival Ecstasy could start at 19,882 miles while a 10-night Mediterranean cruise on Carnival Vista could start at 102,235 miles.

Groupon screenshot

3. Online Marketplaces

Anyone who receives Groupon or Living Social email alerts knows how much of a tease it is to see those polished, low-priced travel packages in your inbox every week. Next time: Don't be afraid to click. Both sites occasionally offer cruise "vacation bundles" that are some of the best deals we've seen. The reasoning? They have short purchase windows and limited availability. You also have only a few travel dates from which to choose, and what's included is quite specific. (You might be confined to cabin categories you wouldn't normally book.)

4. E-bidding Sites

You can buy your vacation… or name the price you want to pay and see if you win. E-bidding sites like eBay, SkyAuction and Luxury Link are sort of like gambling. They're designed for those who don't mind taking risks for a potentially solid deal and have more flexibility in their vacation plans. SkyAuction, for example, offers cruises with a list of dates to choose from. Once you win a bid, you must select your date of choice, and then wait to hear if it's available (you can always cancel if it's not). If it is, you most likely won't know your exact room location or category until your cruise documents arrive, about two weeks before your departure date. (It's safe to assume you will end up with an inside cabin.) On the flip side, some auctions might specify the cabin category or offer the opportunity to pay for an upgrade. While e-bidding sites can be a steal, they don't make it obvious how much you'll need to pay in taxes and fees above your bid price; always check the fine print.

5. AAA

AAA -- America's well-known auto club -- also sells cruises through its travel arm, and rates are comparable to those of travel agents. Apart from AAA's revered hotel and car rental discounts, you can expect some cruise line-specific extras like onboard credit or a complimentary double upgrade -- though these vary based on your membership and where you live. Like other travel agents, AAA offers a sense of security. If something were to go wrong on your cruise, the association's agents, available 24/7, would work directly with the cruise line to handle the issue for you. Where you can win big is with the company's Member Rewards Visa. The card offers a 3 percent rebate for qualifying travel booked through AAA -- which can add up to a decent chunk of cash back when you make a final payment on a cruise.

6. Credit Cards

Credit cards and a world map

Credit card companies don't actually sell cruises, but they do offer certain cardholders exclusive perks and deals that can only be redeemed via their travel agent partners. For example, MasterCard World Elite cardholders have access to a portfolio of onboard credits for various cruise lines -- some of which can be combined with the lines' own promotional offers. To use them, cardholders must book through the company's designated agency, Carlson Wagonlit Travel.

Have a travel rewards card? You can book a cruise with the points you earn for making purchasing with your credit card. Contact your credit card or browse its rewards website for specific numbers of points needed to "buy" a cruise. Cruise lines also offer their own rewards cards, and points earned can be redeemed for cruises, cruise discounts and onboard credit. However, these cards often don't stack up (in terms of what you can do with your points) to the credit cards that simply offer travel benefits.

7. Timeshare Exchange

Exchanging a portion of your timeshare for a cruise seems like a no-brainer. But it doesn't always yield the best deal. Companies like Interval International or Resort Condominiums International (RCI) -- which allow you to exchange "weeks" or points for a cruise -- come with limitations that depend heavily on when and where you wish to travel. For example, you only might be able to cruise to Europe versus the Caribbean on a certain date. It's also important to understand exchanges aren't equal swaps. You'll need to do the math to determine whether or not you can actually save money. Bear in mind: You are also responsible for change fees. Every exchange program is different, so determine what your weeks or points can get you and compare it to other booking methods before sealing the deal.