i meant that in the EU wholesale market , everyone gets the marginal price. It is not the cost of an additional unit, a mwh of renewables is practically free (if paid-as-bid) but gets paid as natgas (because it gets paid-as-cleared)

Yeah but that's how the market pricing works, it's a function of the auction process. Everyone pays the price required to satisfy the demand. See stock opening and closing auctions for a similar process. It feels odd that sellers get the higher price but it makes sense ultimately.

The margin price in that market is the marginal cost of a GW hour by for the last GW that satisfies the load required (demand).