The cost estimator is designed to give you a ballpark figure, and is built using averages from inventory across the globe. So, in short, don’t trust it for pitching to your board of directors.
The best way to get an estimate of reach, plays, etc. is to create a campaign and see the projections it offers. The reason this is more reliable than the cost estimator is that it is making a guess of outcomes based on the boards you’ve actually chosen for your campaign (assuming they’re actively asking for ads).
