Don't forget that some of the less popular headsets work well. Maybe not as well as an A20 but offer much better value for money.
I picked up a pair David Clark H10-13XL ANR for 250 quid "brand new". The minted previous owner didn't like them so I got them for a song having been used for less than 5 hours. Lets face it there are alot of people in aviation with more money then sense so there is some hangar chat bargains to be found.
Having now used them for the last two years I have to say I am very pleased with them and have now sold my too feeble for instructing lightspeed zulus.
Yes they are not perfect - battery life isn't great (5 hours with rechargeables) heavier than bose-x etc but they are more than upto the job far better than any passive headset I have owned and are built like a brick****house so should last me another 25 years or so.