The B-52 requires complete air superiority in the area that it operates because it can't hide from radar except by jamming, so just building a new version wouldn't really work. The B-1 has speed on its side (thought not as much as the original specs) and the B-2 has stealth. The tentatively named B-3 is supposed to replace all of the heavy bombers, though the B-2 will probably stick around for a few decades. That's a reasonable goal, unlike that of the F-35.
It's supposed to use mostly existing technologies instead of planning for advances as happened with (and expanded the cost and schedule of) the B-2, F-22, and F-35. Whether they can actually do that is a giant question mark, but the Air Force is allegedly targeting $500 million to $600 million per plane as the final cost.