Price of retail should more or less be based on based on this factors: base game cost+cost of hard copy+chain of retail distributors+VAT
While digital version on this: base cost+digital distributor cost+VAT
Its just as simple as this. Electronic books for example are priced in similar fashion and i see no reason why games couldnt have different prices for different media they are made on.
Is this system fair - imo yes - alot more than what they are doing right now.