When City overpaid for Grealish last season they already had a title winning side and were looking to improve quite literally one or two areas. If we were in that position then given our resources it might be justifiable to overpay for the luxury of getting your money-no-object first choice pick in a given position.
In our case though, we have near an entire team to build across multiple transfer windows. At that point transfer efficiency becomes vital as overpaying is the difference between improving another area of the team this season or not. And whatever about Rice as a player, he's one of the least transfer-efficient purchases we could make this summer.
There isn't a chance in hell that across all of world football no other midfielder could be brought in to do a high-level job for us in that same position for 50m or less. And opting for that other option could be the difference between being able to sign another first choice player in CB, CM, RB, RW, wherever.
For Rice to justify that not only that extra money over all other options but also that opportunity cost at the very start of a rebuild, he would have to prove to be arguably the best midfielder in Europe. Anything less and it's difficult to justify hamstringing the first step of a rebuild by committing so much of our limited resources into one player.