Try getting a cost for the same quality but made in UK, you'll soon give up if you're not planning to make hundreds  
  
EDIT: 
  
We've been down this route before, remember the Vortech 1 Pipe stuff?... 
 
  
True, but that requires specialist machinery to mandrel bend the piping, as well as supplying the MAF slot as well.  The key is getting a trusted manufacturer, which is why the Vortech pipe fell on it's head.  Making a coolant chamber out of flat aluminium and welded with fittings shouldn't cost an arm and a leg if made in the UK.  No shipping or Customs to contend with. 
  
Have you investigated anywhere in the UK?  £350 for a coolant chamber is a lot of money for a custom item, which isn't even branded. 
  
I could try and put you in touch with a couple of outfits in the UK.