We paid a lot for the flights, they were £366 each (but we will be celebrating my 50th birthday while we're out there so we splashed out!) That's flying from Manchester and staying for 10 nights though. Just looked on
http://www.skyscanner.net and you can get flights for 2 adults and 2 children to Benidorm for just over £500 in total. Hope that you manage to find something nice. We always book flights very early so tend to get the cheaper prices.