The marginal utility of a good refers to an individual’s valuation of the good’s utility (at its margin). In the case of an eBook where owning three or even 300 of the same book is of no more utility than owning one, I think the marginal part of marginal utility essentially becomes redundant and it really just depends its utility. That is, they’ll be willing to pay whatever price for an eBook that is consistent with their valuation of the utility it will provide them with.

The suppliers of the book will set the price based upon what they think the market will bear in a manner to maximise their profits. The cost of producing extra units of an eBook drops to an almost neglible amount and this is taken into account when setting their price. Lets say it costs me $10,000 to produce 100 ebooks (unit cost = $100) and it costs me $12,000 to produce 12,000 ebooks (unit cost = $1) – in the first scenario my selling price needs to be $100 + profit, let’s say I choose $140 per book and I then make $4000 profit. However should I set my price at $20 per book with the aim that I’ll sell 12,000 books I now make $228,000 profit ($19 x 12,000). Of course in the real world it will be impossible to know up front how many we’ll sell at any given price and it is the job of the entrepeneur to forecast such things. The price can also start high and then it would pay to progressively drop it until I sell more and more (given the additional unit cost ends up so low).

The entrepeneur would have access to info that could help them in this forecast, for example, how many units of an ebook with similar appeal have been sold at a given price. It is just a game of forecasting and then profit maximisation (sounds simple but obviously forecasting can and is in many cases wildly wrong).

Don’t know it that addresses your question or not but hopefully it is helpful.

Your comment seems to imply that since costs of production for additional units becomes so low to the supplier that

That said, the prices of the modern digital media market are not the equilibrium prices: I’m willing to wager that the prices here are the most inflated prices of any market that’s ever existed.

Bastiat would argue that wheat, like water and air, had a constant utility but a fluctuating or marginal value.

Two interesting points: contact with the real world outside of academia was an essential ingredient in his discovery; and, the dire economic conditions triggered interest in his discovery.

Conclusion: The educational outreach of the Mises Institute and the widening exposure of searching minds to Austrian economics during these truly cataclysmic economic times bodes well for the advancement of economic science!