I'm surprised at how little has been said in this thread from a teacher perspective. Children being off sick or just bunking off is bad enough, but parents willingly taking their children out of education for a week or two to save some money puts a lot of unnecessary pressure on the class teacher as it completely affects the planning and structure of the lesson and the ensuing disruption that having to help a student catch up on work results in.
As a trainee teacher I'm experiencing first hand how awkward it is to be trying to teach a whole class a particular thing, knowing that those that weren't there last week are getting even further behind, and it'll take the whole lesson, if not more, to get them caught up.
Children should be in school during term time. End of.
Oh, and if you're looking for cheaper holidays, try sending your kids to an Academy school. a lot of academies are changing when their holidays are so that they don't coincide with regular half terms and easter etc.