I didn't know CR7 had such a huge salary, I thought he had a salary of around 100mil and if your info is correct then Ben Jacobs is right and the Saudis are already looking for 350mil for Vinicius. To be honest I'm not sure that Vinicius will be as marketable as Ronaldo in terms of marketing, because even despite his age Ronaldo was recognized as the best player in the world for many years and only Leonel Messi could compete with him.
So if I were the Saudis, I would not hurry to give such money for Vinicius, or it may turn out like with Neymar, who played 5 or 7 matches per season between injuries, besides the character of Vinicius is not the easiest.
Apart from all that, you can't compare Vinicius Jr. with Cristiano Ronaldo. Even though CR7 is now one of the oldest active professional footballers, he is still one of the most popular and best-known footballers (if not the best-known together with Messi). Vini Jr. is not even half as good as CR7 was at his age and he is certainly not as popular.
The Saudis can certainly pay >300 million for him but the question is whether it will pay off?
Vinicius can be a great player, no one can deny that. However, he can't be a player who single-handedly carries a team like Cristiano Ronaldo. Sure, he can do it in some matches, but he can't achieve the same level of success in countless matches. Cristiano Ronaldo and Lionel Messi are exceptional players in the world of football. Players like him rarely come along in the sports world. Therefore, expectations are high for every player compared to them, but they can't meet those expectations.