The airline industry is a maze of rules and regulations, but you can help avoid such unpleasant surprises by familiarizing yourself with the way airfares work. The least expensive fares usually have advance purchase requirements. You might possibly save a few dollars by waiting, but you could also risk paying hundreds of dollars more. Also, even if a sale fare appears at the last minute, chances are there won't be availability for the dates and times you want to travel. Even if you are able to meet all the restrictions of a fare being offered, in order to purchase a ticket at that price you still have to find availability for the dates and flights that you want.
Airlines basically allot a certain number of seats for each economy fare level offered.
So even though there may still be plenty of seats in economy class on a particular flight, the cheaper seats may already be sold out. Most of the lower-priced fares only allow for a stay of up to 30 days. Shortening your stay by a few days to remain within the 30-day maximum restriction or lengthening your trip to include a Saturday night stay could mean substantial savings. Travel seasons - Fares to most destinations can vary drastically depending on the season of travel. Basically, expect to pay more if you want to travel when everyone else does.