Welcome to the club.
But.
That is considered proprietary information and is always closely guarded by companies.
Unless a rogue employee reveals it, or someone hacks their servers ( I am not Henry II, please do not do this. ), we will never know.
I know people who spent $30,000 USD the first 6 month of Magic the Gathering ( btw they often got the money back from reselling). I have teammates that quit Empires after they got their credit card statements from chasing a hero that have similar disposable income. There are accusations of old Zynga bypassing Google and Apple to keep more of the money.
So in the end, who knows?
The biggest I have seen on the forums:
(What exactly is a Gacha? (Read before posting things about "unfair pulls") - #375 by KLinMayhem)
I have heard other claims, but none I have complete trust of the amounts.