Let' s assume that there are no restrictions on what can you buy in GTA Online. How much GTA$ would it cost to buy all properties, apartments, garages, facilities, bunkers, hangars, arcades, clubhouses, warehouses, vehicle warehouses, biker businesses, nightclubs, CEO offices, one of each vehicle, clothing, snacks from shops, guns. All the stuff without upgrades(no extra design for properties, no upgrades on businesses, no mods on vehicles etc.).
The current consensus is that it would take $703,307,823 GTA$ to purchase all of the content available Grand Theft Auto Online.
You can view the calculations in Pyrerealm's video:
If you use shark cards to acquire this money the Megalodon shark card is the best value at $99 USD for 8,000,000 GTA$. This means if you would need to purchase 88 Megalodon Shark Cards to have enough GTA$ to purchase all of the game's items. At $99 USD for each Megalodon Shark Card that's a $8,712 USD investment into the game.