This doesn't add up. If the average person spends US$8600 per year (which they do), total world marketed energy consumption is about 500 quadrillion Btu per year (which it is), then they are paying 39¢ per kilowatt-hour.

But energy doesn't cost anywhere close to that much. http://www.bloomberg.com/markets/commodities/energy-prices/ says current electricity spot prices are around US$40 per megawatt-hour, which is 4¢ per kilowatt-hour. Crude oil is currently around US$80 per barrel, so assuming 0.8 g/cc and 45 MJ/kg, that's 5¢ per kilowatt-hour. (http://www.eppo.go.th/ref/UNIT-OIL.html says I'm low by about 10% where it defines "Barrel Oil Equivalent".) Coal is even cheaper.

Your logic has two problems that lead to this discrepancy.

First, when it bottoms out in a barrel of oil or a lump of coal being bought for some price, it pretends that the money disappears at that point. Actually, however, the money paid for the lump of coal is paid in dividends to coal shareholders, in salaries to coal miners, in interest to Chase Bank, in expenses to Caterpillar for tractors, and so on. These recipients of the money then turn around and spend, by your logic, almost 100% of it on energy. So actually energy accounts for almost 200% of the cost of everything. But it doesn't stop there. 300%, 400%, ∞% of the cost of everything is, eventually, energy.

Second, it doesn't apply uniquely to energy. It applies equally well to, for example, cheese. Maybe only 2% of my own earnings are spent directly on mozzarella and Swiss, but when I pay someone to do a service for me, 2% of what I pay them also gets diverted off to the immense dairy octopus, and so on at each step of the chain, until after only 228 steps of exchange, 99% of the world GDP has bottomed out in one nice wheel of Gouda or another. Thus we can deduce that ultimately the price of everything is some multiple of the price of cheese, because cheese accounts for almost 100% of the cost of everything. (Ignoring, as you did, externalities, the most glaring of which is government subsidies for dairy farming.)

A much more sensible approach, at least when looking at the economy as a whole, is to divide the amount of energy consumed into the total value of goods and services produced in the economy. Using the numbers above, this comes out to about 13%. That is to say, with this method of accounting, energy accounts for about 13% of the cost of everything.

If you want to do this kind of accounting on a per-product basis, I think you have to start by deciding when you're going to stop tracing back the value chain. If you only stop when you reach a particular commodity, whether it be energy, cheese, or human labor, then you will discover that, tautologically, that commodity accounts for 100% of the cost of everything. If you add some more commodities, or restrict yourself in how many steps you go back, or add temporal discounting (it may take 50 years for 99% of the peso I spend this week to bottom out in a tasty block of Monterey Jack, after all) then you may get a more interesting answer. But it will depend on which choices you made.

There is some discussion of different approaches to this problem at https://secure.wikimedia.org/wikipedia/en/wiki/Embodied_ener...