According to below ATO report:...

According to below ATO report:

http://igt.gov.au/files/2015/07/Review-2015-IGT-Debt-Collection.pdf

"Between 31 December 2011, the ATO had referred approximately 1.8 million debt cases to EDCAs valued at approximately $7 billion. The EDCAs had prompted the payment of approximately $2 billion (29.1 per cent) at a cost of $54 million to the ATO." p.138

Around 250m worth of debt was referred to four collection agencies in 2014/2015 compared to 514m in 13/14 and 538m in 12/13 (p.164).

According to a study by ATO, the cost for Collection agencies to collect $1,000 is $7.64 in 2013–14. (p.159)

Rough estimate based on above data:  Collection agencies charged ATO around $27 for every $1000 collected. It costs them around $7.64 to do so. Fairly good margin imo.