We were in the Balkans in August/September 2012 on Irish registered bikes, insured with Liberty (formerly Quinn). Green card cost €50 and covered Croatia, Albania and Macedonia.
We crossed into Bosnia at Brod in the north. Initially we had problems buying insurance because it was a Sunday and the office was closed. Eventually we got someone to sell us insurance at €36 for 7 days.
Crossed into Montenegro coming from Dubrovnik, insurance cost €10.
We entered Kosovo from Rožaje in Montenegro. Kosovo is not part of the green card system, insurance was €15.
Interestingly leaving Macedonia we were asked for our insurance/green card at the exit border, when we were heading into Bulgaria. All other exit borders only wanted to see passports and registration documents.