What % Of Revenue Do You Spend On PPC Ads?

It seems like some sellers have a near limitless ad spend, others don’t like to spend a penny at all. I know it is totally margin and category/product dependent, but I’ve always struggled with what is too much to spend and what is too little. As organic traffic seems to be dropping dramatically, it seems something of a quandary.

So I’m curious about what % of revenue other sellers spend on Amazon PPC Ads?