Klumpen0815: Fair prices for works of art are an illusion. It's impossible to determine the real value.
Purely mathematically, the value of a work of art is the cost of producing that art (including cost of work) divided by the number of copies of that work of art. So if a $60 game costs $60 million to make and distribute, and if 1 million people buy it, it's a fair price. Each copy produced reduces the nominal value of each of the other individual copies. Revenue generated beyond that is a form of economic "goodwill", as the value then fluctuates depending on supply and demand.
Of course, the "cost" of making a game can be accurately gauged when made by registered companies, because every creator - including the managing director/CEO/general head honcho - gets a predetermined salary or wage that is accounted for. It's less clear with games made by bedroom coders who develop in their free time, don't pay themselves a wage from their allotted budgets.
Again, purely mathematically, because we cannot stipulate how much the creator's time, creative effort and knowledge are worth here, it could be argued that the value of the developer's efforts is essentially an unknown that we calculate after the fact. So if a bedroom-coded game generates $10,000 in revenue after deducting stuff like development software licences and electricity, what's left is essentially the coder's salary. If we know how many man-hours have been put in, we have a general understanding of the worth of the developer's efforts.
It all sounds cold, mechanical and heartless, but it ultimately provides us with a baseline from which we can estimate what a game really is worth. Ultimately, if you cannot quantify cost as an absolute, you can only quantify it on the basis of demand and what people are willing to pay to satisfy that demand.