Here is an Astro R replica for £250
http://www.infinitymotorcycles.com/product.asp?ProductID=9&ProductName=Arai%20Astro%2 0R%20Replica Gotta agree with Arai being my personal top choice.
For a quiet helmet though the BMW/Schuberth seem very good.
Infinity do them as well so here is their full listing instead of me searching around:
http://www.infinitymotorcycles.com/products1.asp?start=1&products=87&DepartmentID=125 &manufacturer= Cheers - Frank