Yes, Acidophilus would be the proper filler. Also make sure they do not use slow release LDN, if that is the drug being compounded.
It is better to get it from one of the approved compounders listed on the low dose naltrexone web site. But I suppose there is non in Australia.
I do not know the currency conversion but my prescription is about $36.00 U.S. per month. I could get it for a little less from Skips pharmacy, but I am reimbursed for it anyway, and I like "The Compounders" service.
Dan