For a monolith of any nontrivial size, you're talking anywhere from weeks to months of years of engineer work, and those are engineers who also won't be delivering new value during that time. And if other teams are still delivering new features into the monolith during that time, now that's more work for the team whose job it is to break apart the monolith.
So anywhere from tens of thousands to millions of dollars is the cost.
Whether you call that exorbitant is up to you and your department's budget, I guess.
