With your budget you could get a seriously nice house in one of sevenoaks surrounding villages, Westerham has quite tight planning laws as it's a very old village, so not much scope for development. If you want better odds of devolping a property, Otford has a lot of redevelopment potential. I'm working on a couple of sites where houses are either being extended or completely knocked down and replaced. Prices are rising too as it has its own station with direct links to london and large number of new "top spec" developments