City's salary outtake isn't that bad compared to the other big clubs. Your biggest earner is De Bruyne... and he's only 350k a week, and then it's Sterling. The rest of the team is on like 250k or less. I think you pay around 125m a year for your whole squad. As I said, it isn't that bad. You can easily afford to give Messi a decent salary and it won't kill you in regards to the FFP. Besides, you can sell Mahrez to free up some of the salary, and you can easily get around 40m for him. And as I just said, Messi won't be getting anywhere close to the salary he had with us. He'll more than likely only get 50% of it.
You're in a much better position than PSG to get Messi; PSG just lost 200m due to COVID, and they also lost a lot of money due to their TV deal. They can't afford to have all of Messi, Mbappe and Neymar in their team, especially with potential new contracts from Mbappe and Neymar. If anything, PSG probably has to release or sell players just balance the books in the summer.