I think the complaint is saying your targeted ads are higher than they naturally should be because google is using monopoly power to raise prices.
So google raises prices, companies pay higher prices and then charge more for goods. This the harm can be calculated by comparing the price of ads under monopoly vs ads without monopoly and then multiplying by some average margin over cost.
So google raises prices, companies pay higher prices and then charge more for goods. This the harm can be calculated by comparing the price of ads under monopoly vs ads without monopoly and then multiplying by some average margin over cost.