I don't have any numbers, but I would not expect the median sale price to be anywhere near $50. I'd expect there to be more sales of <$30 games, as a percentage of revenue, than >$30 games. And the cost of distribution goes up relative to the cost of the game as the sale price goes down.
Assuming the sale price of the game in the OP's example was $10, distribution still cost less than 3%, and paypal goes up very slightly because of the $0.30 base charge, but the main fee is percentage based so it doesn't change. So even for a $10 game we're looking at less than 9% in total.
This example is also using s3 retail pricing and paypal retail pricing, which already factors in profits for Amazon and Paypal.
None of the big marketplace's costs are anywhere near 30%.
