Airfare tends to be the most cost-prohibitive (expensive) part of planning a vacation or trip. Plus during the course of a day, prices fluctuate depending on availability. And with delayed flights, over-crowded cabins, excess fees and no free food, it�s surprising that airlines are able to charge such high ticket prices.

Despite the abundance of meta-search engines like Kayak, Google Flights, or Fly.com and online travel agencies (OTAs), finding the lowest priced airfare is still a tedious process. That�s because prices change minute-by-minute, and it takes time to find the cheapest price.

Doing research is only one way to get a cheap ticket, another way is to shop in the �magic window.� Prior to 28 days before your trip, ticket prices are pretty much the same. But during the period of 18 to 28 days prior to your trip, prices are at their lowest. This time-slot is your magic window for booking. Domestic fares bottom-out exactly 21 days before departure.

The last 18 days prior to your trip, prices start ticking up. The average fare increases 5% two weeks before departure, with fares increasing 30% from their lows the last seven days before departure. International fares don�t have as much fluctuation; 34 days before departure, fares are only about 4% lower than the average at six months before departure.

Be sure to reserve your hotel suite when you book airfare. As a general rule of thumb, the more you can tack-on to your vacation package upfront � even including things like meals and tours � the better the savings over separate do-it-yourself pricing.

When booking a package deal, OTA�s are better able to package these deals than airlines. You can save an average of $525 on a vacation �  with an average of $1,000 saved for weeklong vacations to very popular destinations through an OTA.

Airlines announce their sales on Tuesdays, competing with each other and unveiling their latest fares for the next few months. Mid-day Tuesday to late-day Tuesday or early Wednesday is a good 24-hour sweet spot when you can find the latest sales. The airlines also release their last-minute weekend deals on Tuesdays, so flexibility is your best friend for booking airfare along with a willingness to go where the bargains are.

Departure time and day matters. Wednesday is the best day to depart, followed by Tuesday and Saturday. Experts cite savings of up to 10% when traveling midweek to midweek. For a weekend trips, you�ll find that airfare is cheapest when you depart on Saturday and return on Monday.

Flying during certain times can also reduce your airfare bill. The very early morning flights, particularly if you�re going on a leisure vacation, tend to be less expensive than midday departures. Plus these flights usually have the lowest risk for delay or cancellation, since the plane and crew are already at the airport. Overnight flights can usually be good bargains, as well as late afternoon or dinner flights.

Special tip:  When you�re doing your search, don�t initially specify departure times. This way, you�ll be able to see the time of day that really is the cheapest to fly.

Flights from smaller airports can be cheaper. Experts also suggest looking at fares for airports within a reasonable radius of your destination. Large airports are sometimes monopolized by the larger players. Savings for flying into a smaller airport may justify more time in the car spent driving to your destination.

Consider one-stop as opposed to non-stop flights. When the stop is in the airline�s hub city, it can generate some dramatic savings and thus lower fares. When traveling with small children, time during a layover may be a welcome break from the plane.

One-way tickets can be a bargain. Buying two one-way tickets from different airlines may be cheaper than a round-trip ticket. Many meta-search engines will do this for you, such as Kayak�s �Hacker Fares.�

Continue to check fares after you book. If fares drop within 24-hours after you�ve obtained your ticket, you can cancel your flight without paying a fee or penalty, according to Department of Transportation regulations. However, the flight must depart more than a week from the time the ticked was procured. If fares drop outside this 24-hour window most airlines have a credit or refund policy, but they may charge a fee.