It would depend on implementation eg stringing a wire between houses to share 12 or 24 v power supply or if it needed to be 240 v and thus a truly licenced installation. If charging stations were built with the ability to also accept power as well as deliver then the cost could be very small to add power to a network either local or national. There is always a cost but some would be very small in comparison to others. Even nationally if the cost was shared between all consuming entities the cost per user could be quite low in comparison to the cost of the actual power consumed.
A version of p2p sometimes operates in small communities ie someone has a generator, the rest of the community run power leads to the generator and pay an amount for the fuel and maintenance. This shares the cost but all benefit from the power supplied. I have witnessed this in operation. While it isn’t what a lot of us would accept, when it is a choice of some lights and a radio or living by firelight they often choose the former rather than the later, the benefit outweighs the cost.
Are there other types of networks that could be used as examples of cost and benefit, well at least in computer terms you could look at LAN, WAN, and the internet as a whole. They all deliver benefits, they all cost, but for the most part we would say it is mostly to our benefit. I think that the maintenance cost of a national power p2p network would keep the network infrastructure working but the benefit of shared power and not having to rely on a single or very few sources of that power could have vast benefits for our populace. Looking at 2013 power bills for Qld the cost of transmission and distribution are about 52% of the bill, for Victoria it is about 30%, NSW about 60% from https://www.energynetworks.com.au/sites/default/files/electricity-prices-and-network-costs_2.pdf
