$420m, Google says. You can almost buy two 747-8s for one B-21, and the 747s get used all day.
A b21 can be used everyday too?
Then again, perhaps maintenance of a stealth bomber really is horrendous enough that it wouldn't be able to fly sorties "every day".
But basically I read GP cooment as an apples to oranges comparison (since you traditionally wouldn't drop bombs using a cargo aircraft, and wouldn't airlift cargo with a bomber.)