A survey a few years ago found that about 40% of vacationers financed their travel plans with plastic -- and more than half didn't pay off the tab right away.

We don't want you to stay at home and mope, but if you can't afford to pay cash for that cruise/camping trip/Civil War reenactment, ask yourself if you're willing to pay double for it. Because that's what it'll cost if you pay just the minimum amount due on your credit card.

Given that travel is one of the biggest budget line items for many folks, shopping around for savings is worth the time. With the average family spending more than $1,600 for their summer vacation, according to a survey by Visa , trimming costs by just 15% amounts to $240 in savings -- and that's just for the summer trip.

Below are some general tips on booking the lowest-cost airfare. We've hit the high points, but for much more nuanced advice, check out the Fool's Best Travel Spots/Tips board for tips from seasoned travelers and sightseeing advice from locals.

Five ways to catch a cheaper flight
Everyone knows that advance planning is everything when it comes to travel. Nowhere is the savings more significant than when shopping for airfare. The bonus to arranging your getaway now is that you can solidify your plans before all the aisle seats are taken (and have something to motivate the kids to do their chores). Here are some websites that will help you get there -- wherever that may be -- for less.

Track fares for a while. Many websites will keep an eye on airfare costs and alert you to the best deals based on your travel criteria. Check out cFares.com to search airlines, travel wholesalers, and agencies (for a membership fee, it also offers a name-your-price feature); and Airfarewatchdog.com for cheap flights before they hit the major travel portals.

Do comparison-shopping diligence. Make sure a deal is really all that by comparing your quotes with those offered directly by the airline. In addition to the biggie travel sites like Expedia (Nasdaq: EXPE) and Orbitz (NYSE: OWW), there's a plentiful list of aggregators to choose from like Travelocity.com, Hotels.com, and Travelzoo , which delivers its deals through its website and its Top 20 email. Other aggregator sites include Kayak.com, SideStep.com, Yapta.com, 1800FlyEurope.com, and I'mWillingToRideInCargo.com (kidding on that last one).

You might encounter some fares that require you to pick up the phone and contact the agent directly. Do it -- that's how I got a direct flight to Paris for half of what it cost on another website. Also, there's always Priceline.com (Nasdaq: PCLN) and its name-your-own-price policy.

When browsing, keep in mind that some airlines, like Southwest Airlines (NYSE: LUV), might not even offer their listings through larger aggregator sites. And once you've selected a flight from an airline, double-check at the airline's own website to see if you can avoid booking fees or can score a lower price on the same flight. Continued...