Get an old second hand pair of Dave Clarkes or similar for £40 and tear out their innards and replace with a set of ANR electronics from here:
http://anrman.co.uk/The cost of the conversion when I did mine was about £120. You can pay a little more and Richard will do the conversion for you. The reviews have it as being on a par with a Bose X headset. Yes, I know the A20 has been out for a while.
I did it and I've had sterling service from my set for the last 7 years. I think it's still the best value headset going, though you can now buy an ANR headset new for about £200, but I've no idea if they're any good.