Just had e-mail back from Balkan - apparently whether or not you have to pay this deopends on when you booked. we booked last year and they say:
'we have covered this for you we will not be contacting you for any extra payment'
... well, every little bit helps!
If you are booked via a package holiday they have to absorb the new tax. However if you are on a flight only basis, it is up to the airline whether they charge you the extra tax or not. Yvette