you want to be very careful with super strats, sambo- the cheaper ones can have cr@ppy double locking trems that won't hold tuning very well, won't have good sustain, and will generally be more bother than they're worth.
Machinehead are selling a washburn x40pro for £379, with a schaller trem (good!), and duncan pickups (distortion and '59, i think). Not as good as BK's, but much better than most pickups on guitars of that price, and good enough that you wouldn't have to rush out and immediately upgrade. I haven't tried it, but going by specs, it should be good, unless it was made by an arm-less monkey. Only reason I didn't go for one is it's 42mm nut width, I prefer 43mm. Alder body.
The Ibanez s470 is also worth a look- has a zr trem, which is good, although i tried one (unplugged) and thought it played well (43mm nut, lol), but i've heard that the quality control isn't so great, so you'd want to try it. Around £340, i think. Pickups won't be great (it's an Ibanez, lol). Mahogany body.
If you can get a little more, an ibanez rg1570 would be worth a look. Again, pickups won't be great, but, if you get one of last years, it's japanese-made, edge pro trem (good!), super fast neck. basswood body, though, so it's very much voiced for shred. the 1570 would be my pick, but that's me. Also, if you go second hand, a 570 is basically the same thing, but with an edge bridge (good, again).
What type of tone are you after with it? Superstrats rock, by the way, I love them. :B
You should maybe have put this in the guitars forum, too :D