Family houses in Beckenham in the catchment area for Langley start at about £850k - anyone moving there just for the schools would probably find it cheaper to go private, unless you can downsize. I have a friend who traded a huge six-bedroom Victorian villa in Penge for a three-bedroom thirties semi in Beckenham to get into the catchment.
Not all secondary schools operate on a catchment policy, so moving is not always necessary. My kids go to a mixed school in Streatham. Kids tend to travel much further for secondary school than primary. Buses are free, and the Overground costs £1 per journey. The only downside is that their friends are also more spread out, but my eldest (aged 14) can now confidently negotiate buses, trains and overground to meet her friends in town or in Croydon, Streatham, Crystal Palace or Bromley. She is much more self sufficient than her friends who go to school much closer to home.
It's hard to imagine when your kids are in primary school that sending them to a secondary school that is not 'local' can be a good thing, but it works well for us.