As good a place as any to start is to look at Skyscanner and see where you can fly to from a nearby airport, then have a look at flight prices to identify the cheaper routes. If you view flights for a particular route for a month you sometimes find a random one that is loads cheaper for no apparent reason so can plan around that
Alongside this look on websites like Home and Away or Holiday Lettings websites for accommodation in the areas the cheaper flights go to. Again, you'll soon find that some destinations are way more expensive than others.
That's what I should have said Norbert. I forgot that not everyone plans their holidays like that!
I also get a rough idea of prices on Booking.com, but then shop around to see if it's cheaper to book direct. Owners Direct is another good site for accommodation. Don't be afraid to book flights with different airlines either. We're flying out with Ryanair and back with Monarch, saving about £30 pp.