A couple of hundred for frame and forks will get you
almost any of the framesets you're looking for excluding the exotic things like Gen 1's, trickstars etc.
My advice would be to decide what you want first, then adjust your budget accordingly.
£200 will get you virtually any Haro '85-'88, a Streetbeat (or 3), maybe a later GT pro performer. If you're after a Curtis, they pop up every now and then, just keep your eyes peeled (I just picked up a complete Curtis for £125)