It's easy with coins that have premine (with or without ICO), as the premine must cover all operating costs for whole lifespan of the coin. As such premine divided by total operating costs equal to value of one coin.

For coins without premine or ICO, the amount of mined coins per month need to cover the mining related expenses, so value for one user can be quite different than value for another user. For members of development team, value of mined coins need to also cover expenses related to operating the coin infrastructure.