Jools it sounds like you're looking for a BBC type sound.

A big second hand pair of harbeths perhaps, spendors.. something along those lines I reckon for the money.

Or how about an audionote kit?

I really think you'll like the mids on these, its generous like a big BBC speaker.

http://www.hificollective.co.uk/kits/speakerhome.html

It would come in on budget if you've got DIY skills.. or you could pay someone to make it for a couple of hundred.