i'd probably go looking around the £350 mark myself!
seems to be a stepping stone in the market from an o.k bike to something with an actual purpose.
£300 will get you a fairly decent package, tri-moly or chromoly frame, o.k ish componentry, but for and extra £50 will get you into full chromoly frame fork bars, sealed 3pc cranks, sealed cassette wheels, decent geometry, and 'named brand' componentry. an all round package that'll 'last the distance'. if you look at history, to get a bike of this kind of spec in 1995 would cost around £900
something like this would be my weapon of choice
http://www.rideskateboardingbmx.com/WTP2008TRUST.html