Flights are cheaper now than say five years ago. In the current climate I'd be looking to pay no more than £500 and I'm quite confident I could get a fare with one of the better airlines for that price. That's Heathrow to Manila by the way which usually is the cheapest route.
The most I've paid is £630 (June 2012) but I left the booking too late. Cheapest was £375 last November.