Why would an ebook be cheaper? Is it not more convenient? Price comes from value, not what it costs to make so being easier to produce has nothing to do with the price (well, except the price floor).
But some people who don't get how markets work think prices are: how_much_work_I_did+how_much_materials_cost+profit_amount_I_want. It's not. The item is priced based on the value it is perceived to provide.
Things are priced by the buyer according to perceived value also, but using a different equation. a sale occur when the two points close enough that either or both parties are willing to adjust their price point to make the sale.
The seller "prices" the goods at marginal cost + profit. The buyer decides if there is enough values at that price for her to make the purchase.