I see it as Ronaldo's strong reason to keep his existence even in the top competition of club's level. There's nothing wrong for him to wish he can play again in CWC.
I heard that the prize for winning one is massive too, although I'm not sure if that money will go to the players instead of the club. That being said, it is possible that the player and the club draft a contract with add-ons, offering extra bonuses when they appear in the Club World Cup, score goals, or assist, and so on. I also don't get why it is shameful to take a lower salary. It is not like he's begging someone if he accepts that deal anyway. In the end, it's just business and a desire to play football.
I don't think Ronaldo will care about the price. His intention is obviously playing at CWC. See no more than it, and importantly, he will fight Messi once again. This will bring back the old memories about how intense the compettion between him and Messi.