''give them AU$50 apiece''
that will hardly compensate for the hours of time wasted (even at minimum wage levels), the frustration, the problems caused by not being able to print something important.
It is also not enough to discourage HP from pulling a similar stunt again.
Compensation should be a minimum AU$500; or more if the customer can show consequential loss.
HP is acting as John Deere does with tractors. Both are despicable.