[libertine]

Assuming you only rely on paid media, yes, you'd need to pay for visibility (arguably through one or more of the 3 main players you've mentioned), or invest in other forms of earned and owned media.

But paid media is a small fraction of the marketing mix when it comes to sell and distribute a product - doesn't matter if it's software or a physical product.

Being unreasonable or not should be up to anyone of evaluates the distribution/sale/communication channel. But I'd limit this fee to be for the "access" to the only distribution channel - because you don't have a guarantee of clicks/impressions/downloads or any media KPI for that fee.

The CPC of a paid keyword is a subset of many subsets of media alone.