From what I've read (which I guess is largely speculation, although by people more familiar with the topic than me), the B-21 doesn't really push the envelope.

From what I've read (which I guess is largely speculation, although by people more familiar with the topic than me), the B-21 doesn't really push the envelope. The only really new thing is the airframe itself, but that largely piggybacks on stealth technology development over the past several decades (RAM coatings, shaping etc.) compared to the B-2, and not some entirely new R&D done only for the purpose of the B-21 program. The engines apparently come from the F-35, but obviously without the afterburners (an entirely sensible choice considering the F-35 is supposed to be manufactured in very large numbers and supported for a long time into the future). Electronics is supposedly stuff already developed. Etc. etc. If true, then yes, the B-21 has potential to be relatively cheap to build and operate.