On Sky News George Brandis draws our attention to another quirk of the constitution:
Until the Parliament otherwise provides, any person declared by this Constitution to be incapable of sitting as a senator or as a member of the House of Representatives shall, for every day on which he so sits, be liable to pay the sum of one hundred pounds to any person who sues for it in any court of competent jurisdiction.
So that appears to be over and above any amount of salary etc. that he would be liable to repay to the Commonwealth.
I suspect this amount would be payable to those people who could reasonably argue that they were displaced by the person sitting in the parliament while being disqualified to do so – although the constitution does clearly state “any person”.
Anyway – long story short: Using the RBA calculator £100 in 1901 would be $14,757.13 today. So that works out to 9 years*365 days*14,757.13 = $48,477,172.05 as a rough guess as to how much Scott Ludlam is up for in compensation. Now we could argue that the Senate doesn’t sit every day so that figure could be a lot lower. Others might argue that £100 remains £100.
But the point is clear – the Constitution created a punitive regime for any person who sat while being disqualified. This is not a debt to the Commonwealth that can be waived by the Special Minister of State (Scott Ryan in this instance) but rather a civil action that can be brought by “any person” (but I suspect the court would interpret that as being someone who might otherwise have been elected).
Update: Gavin Putland, in comments, points to the Common Informers Act of 1975 as effectively repealing section 46. Looking at that Act it seems that section 46 was established as an incentive mechanism to check up on the status of sitting politicians. Now that the £100 incentive fee has been removed we can have foreigners sitting in our Parliament for 9 years before anyone bothers to check up on them.