The idea that capitalism is either a natural or optimal system doesn't stand up to much serious scrutiny. If you're referring to "cost" in terms of energy cost

The idea that capitalism is either a natural or optimal system doesn't stand up to much serious scrutiny. If you're referring to "cost" in terms of energy cost then yes there is always some amount of energy which needs to be put in to get energy out, with the result being the net energy gain. For other forms of energy, such as bio-fuels, the net energy gain is presently smaller but this does not invalidate these technologies. As the complexity of extracting oil increases its net energy gain will reach parity with other energy sources, and then begin to lag behind them. The economy - with all its foibles - will eventually back the winners out of pure necessity.