If Boeing had only build 21 B-52s, accounting for inflation they probably would have cost more than that each.
B-2s "cost" 2 billion dollars apiece in that the procurement program cost 44 billion dollars for 21 aircraft. 25 billion of that was one time R&D costs - or more than half the price of each aircraft - and most of the rest of it was production inefficiencies of such a short run.
The full planned run of 133 aircraft would have cost about 80 billion - 600 million apiece, or a little more than 1/4 the price per unit.
We spent 60% of the original pricetage and got 15% of the original product. Pentagon cost cutting at its very best.
The B-2 doesn't cost an additional $2 billion each to make. You are just repeating the numbers the DemocRATS use to justify the production halt. The $2 billion figure includes the fixed R&D costs allocated to each copy built. Quite a few Republican Congressmen are interested in building 40 new tactical B-2 bombers at a cost of $700 million each. The differences would mostly be due to less extensive EMP shielding in a tactical only version.