Before going into deep talk need to understand few things which are also important top four clubs in Saudi League belonged to PIF Saudi Investment Fund mean their promoter is one company if any club from these winning they are winning just because they are not caring about few things.
Al Hilal and Al Ittihad winning trophies and Al Nassr getting fans for Saudi League mean their task are completed if Al Nassr is not winning it's never been a problem for them Cristiano Ronaldo is the charismatic player who is bringing more fans and this is also helping them for having their targets achieved.
Money has never been problem for Saudi League their main target is always bringing more fans and better exposure of this league around the world increasing quality and competitiveness is also good.
You got it right, the Saudi Arabia pro league has already achieved their aim , which is to promote the league to the world visibility and the arrival of cristiano Ronaldo was enough for them. They got the desires audience and viewers. As we speak the league is still attracting more young players from Europe leagues. The league has become a threat to Europe leagues, they have the funds to get any players of their choice. In recently time the league has become more competitive and interesting for the players.
On many occasions Cristiano Ronaldo has said the Saudi Arabia pro league is bigger than the French league because of the competitiveness of the league, in the French league PSG is the only big team while in Saudi Arabia pro league one can not predict who will win the titles at the end to the league, the competition between Al-nassr, Al-Hilal, Al-Ettifaq FC and Al - Ahli is giving the league more views and fans. That's why they can pay Cristiano Ronaldo any amount he demands for his contract, because ok ney is the not problem of the league, they want to be a football nation and they will keep signing influencer footballers til they achieve it.