Just to give you a sense of what is considered a good deal around here:
Europe-USA: Generally less than $500 roundtrip in Economy, most typically $200-400. Originating in London may be a bit higher.
In business, for Europe-USA good deals are generally less than $1500, usually varying between $1000-1800, although <$1000 happens a couple of times a year...And these are USD, not GBP.