Before you start shopping Halloween costumes, you might want to fire up the computer and book your Thanksgiving and Christmas airline tickets.  Priceline.com reports that some of the biggest U.S. airlines cut back on flights earlier this year, and is predicting higher holiday airfares and more limited ticket availability for the 2011 holiday travel season.

Already, the national average for Thanksgiving airfares is $400, up 4% over last year.  The national average for Christmas airfares is doing better at $475, up 1% over last year.  Priceline calculated the average airfares for both holidays based on published price airline tickets booked by its customers between July 1 and October 4, 2011.

Earlier this year, major airlines told the media that they were planning to cut their 4th quarter 2011 flight numbers.  Delta said it would reduce its flights by 4% to 5%, while American reduced its Tuesday, Wednesday and Saturday flights by approximately 4% starting last August.  United and Continental, which have merged, expected flight reductions of 2% to 3% for domestic flights for 2011.

“With holiday airline tickets, it’s the same pull and tug of supply versus demand except, this year, supply will be down with some of the major airlines flying fewer seats,” said priceline.com’s Travel Ekspert, Brian Ek.  “It’s always possible that travelers may balk at higher airfares and airlines will respond with sales.  However, with ticket inventories already reduced, that’s not likely to happen.  Travelers who want to go somewhere over the holiday season might want to think about locking in their tickets before fares start to rise and seats are taken.”

Airfares, hotel room and rental car rates for the holidays are highly dynamic and subject to change.  To help travelers get the best available travel deals, priceline.com has created a web page http://pcln.com/bestdayst.  The page contains an interactive and frequently updated Best Days To Fly calendar and hotel deals from around the country.

According to Priceline’s Best Days To Fly Calendar for the holidays:

*  The most affordable days to fly over the Thanksgiving holiday are November 19, 20, 21, 24 (Thanksgiving Day), 25, 29 and 30.

*  The most affordable days to fly over the Christmas holiday are December 17, 18, 19, 20, 21, 24, 25, 27 and 31.

Ek also had some additional tips to help find cheaper airfare and keep those travel costs down after the airfare is booked.

*  Pick times of the day that are normally less busy.  Time of day is important.  Travelers will find the most affordable seats departing early in the morning (5-7 a.m.) or late evening (after 8 p.m.).  Mid-day (11 a.m. – 4 p.m.) is a bit more expensive, but still reasonable.  Most expensive are the peak business travel hours (8-10 a.m. and 5-7 p.m.).

*  Try priceline.com’s Name Your Own Price® airline tickets service.  You can save even more on your airline tickets by using priceline.com’s Name Your Own Price® ticketing service.  Visit www.priceline.com/flights and click on the link to use the service.  For help in deciding when to fly or how to bid for maximum savings, check out priceline.com’s Inside Track www.priceline.com/insidetrack.

*  Send those presents on ahead.  You see presents; the airlines see extra baggage and maybe some extra fees.  Not to mention how unhappy the security screeners will be to see those wrapped boxes.  Save yourself the hassle by mailing or shipping presents in advance (after you’ve wrapped them, of course).

*  Weigh and measure your baggage.  Check your airline’s maximum requirements for checked and carry-on bags to make sure you won’t incur extra fees.  Fees can be up to $38 for the first bag and $45 for the second.  Note: baggage fees are charged separately for your outbound and return flights.