For my last game, just over $2M per map. That includes costs of things like first-party certifications.
And please note that multiplayers map and weapons are really cheap to make, so no that's not fair for the customer.
I'm curious as to how much you think it would cost to make a new, balanced, multiplayer map?
Most customers (and sadly too many developers) have no idea just how much content costs.
The simple act of getting a piece of content posted as DLC --- first-party certifidcations and such --- is a six digit figure by itself.