Cost of the B-2 included all the R &D, to quote Global Security.
...."Northrop had estimated that it would cost between $2 billion and $4 billion to reopen the production line, including nonrecurring costs. Each new aircraft would cost about $500-700 million for a production run of 40 aircraft...... In 2001 Northrop Grumman Corporation offered to build 40 more aircraft at a cost of $735 million apiece"....
That included the cost of reopening the line, so deduct $100M per airframe, to get it down to $635M each.
The price of the LRSB? It is smaller and simpler, the risk is lower and tech more proven, and the costs spread over 80-100 aircraft instead of 40, so say another $100M off each aircraft, to about $500-550M each?
"...In the briefing Tuesday, the Air Force announced it will pay $564 million per bomber for the first 21 aircraft, for a total initial procurement cost of $11.8 billion. Research and development for the first bombers is expected to cost $23.5 billion, the Air Force said."
......."The service requested that two independent government cost estimators look at the program. The two groups projected that each bomber will cost $511 million in 2010 dollars on average if 100 planes are built, Air Force officials told reporters on Tuesday — substantially less than the original $550 million target cost set by then Secretary of Defense Robert Gates. This translates to $564 million per plane in fiscal year 2016 dollars."
Oh!!! And, why you may ask, the B-21 rather than the B-3? Well, makes senses as it seems a derivative. But also remember, no-one is allowed to mention the B-3 bomber......