I agree that that much work is worth more than $5 per adventure, however, I am not WotC or Green Ronin or Paizo, I'm just little ole' unheard of me. So as a publisher, who no one's heard of - its hard to assign $19.95 or any other price, because no one's going to buy.

As a "loss leader" that is, something to get buyers into the store to look at my wares, by making a insanely low purchase. I can get people to make a purchase, that might otherwise not want to invest in what they don't know.

On the extreme side, if 5,000 people ordered the adventure (not very likely) that's $25K - certainly a worthy profit. If no one buys, it was an experiment worth the effort all the same.