First off, that negative cost doesn't take into account the massive investment in infrastructure to generate that power.
But it does account for that.
The costs of equipment design, manufacture, installation, maintenance, repair, and power distribution infrastructure, are all indirectly included in the market dynamics that dictate the price — along with more obvious price effects such as instantaneous supply and demand.
If infrastructure were cheaper to build then the instantaneous price would have been even lower (more negative).
Generating methods or instructions for computation by a traditional program (or compiler) would probably fit into this broad category. But actually following those instructions, to perform the actual computation, would not..
The most delightful day after the one on which you buy a cottage in the country is the one on which you resell it. -- J. Brecheux