How much fossil fuel are acceptable to burn, should subsidizes count to the total cost, should grid connections and transport count to the total cost, and what is the time frame? Is the market allowed to freely spike based on supply and demand with no price roof?

The service that the money is paying for is to have a grid that is always producing enough energy for any demand at any given time. Having 10gw/h today but 0 tomorrow is worth close to zero. If people are asked how much they are willing to pay in order to not get disconnected, the current record in spot price are 580.55 per MWh (that is market price before taxes, connection fees, and so on). How long voters would accept a elevated price is a question that many countries in EU saw answered following the energy crisis.

So the best value for the money is the cheapest one that provide the service that people demand when all the costs are accounted for, and that does not cause voters to elect a new governments in order to have it solved.