The B-21, a cheaper version of the B-2, makes more sense as new bomber since it can do the normal bomber jobs and the B-52 job of nuclear cruise missiles.
B-52 engine refurbishment is going to cost $15 billion for 70 odd bombers, or $214 million each. $750 million is current cost of B-21.
https://en.wikipedia.org/wiki/Northrop_Grumman_B-21_Raider
Notice all the references to the B-21 are future tense.