Here is a great way to save a lot of money bidding on Priceline for flights and save 50-60% off published fares. I have seen a lot of people posting that they have been unable to find decent deals on plane tickets but this one way to get low prices on plane tickets.
1. Select my days of departure and return and bid a ridiculously low price ( like $25.00 or something ).
2. Normally priceline will deny the bid however they will present you with 4 or 5 different alternative options such as departing from a nearby airport or slightly alternate dates of travel. Each and every time I have done this, I have scored great deals. I will never book through an airlines website again.
3. You must be flexible. You can depart/arrive on your selected days anywhere between 6am and 10pm however I have found that most of the flights I won have been late morning/early afternoon and arriving in the late evening.
4 The only downfall that I have found it you are usually booked in the lowest fare class thus rendering you ineligible for upgrades/miles.
Some flight could be cheap for weekends in Europe too. I Usually check on Skyscanner and put the date but not the destination for weekends, then I can find the cheap ones for a weekend break. For holidays, if you book in advance or really late you might get a good deal