I suppose I have to ask ... why does avast have a free home version for Windows and not for Mac?
I know that anyone who can afford a Mac must be a rich b*stard deserving to be fleeced of every penny that avast can get out of them ... but there may be a more than a few similar Windows users too.
(In reality ... I just had to face this issue as one of my support group decided to buy a new laptop to replace a vintage machine on which he had been playing with Linux and decided to go with Mac - when they were having a sale - and was disappointed to find that he could not get avast for free on his new Mac)