He's not scoring 40+ goals in the PL, he doesn't even score that in La Liga anymore.
Ronaldo would be a good signing for a team like City, PSG or Bayern that has enough quality for him to shine in front of the goal, he could give them the edge they need to start appearing in UCL finals and winning them and you can't put a price tag on that. But if you take current Ronaldo and put him in the area with current United you would basically burn 140M + wages on a player you can't "feed" on the pitch.
Dunno, feels like Everton getting Pulis as a coach and splashing 150M on Messi, seems logical, but you would be overpaying for a piece your team really doesn't need.