You could use 2 integer variables to work as a 64-bit long integer.
One variable is used to hold 9 digits maximum, so up to 999,999,999.
When this value reaches 1 billion, you substract 1 billion from it and add 1 to the second variable.
This second variable is actually the "billions counter".
When the first variable gets negative, add 1 billion to it and substract 1 from the second variable.
To display the complete value, you can put them behind eachother in a string.
PHP Code:
printf("Total value: %i%09i", variable2, variable1);
Something like this.
The %09i is there to make the second value always 9 digits long.
But remember, PAWN is still a 32-bit language as well as SAMP and GTA SA.
You won't be able to display that value using the normal GivePlayerMoney function and have it display normally on the client.
You'll need to use a textdraw and display the total value as a string onto that textdraw.
But still, you should restrict your economy to avoid such huge numbers, especially for money in a game.
When a player reaches 2 billion, it's easier to show them a message that they should transfer some of their money into a bank-account or vault or whatever you can program into your server to store excess money.
And limit their money to 2 billion.
If they earn excess money without transferring some of their money elsewhere, it's simply gone.
That's how most games do it to protect the player to roll-over into negative values (going over 2.1 billion will get them into -2.1 billion).
Even big-budget games deal with excess money this way.
Either to protect the player from going into negative, or to protect the game from bugs/exploits.
I know about a bug in Aion (an MMORPG) when it still was 32-bit.
Players could buy stuff and the buy-window would count the payment upwards until the values displayed in that window rolled over into negative.
Then after clicking "Buy", the player didn't pay anything, but they became instant billionaires.
Substracting "-2 billion" from their money actually gave them the money, as well as their merchandise they wanted to buy.
You don't want to deal with such bugs on your server.
They converted the entire game-engine and server-package into 64-bit to deal with this exploit.
If they think it's stupid (they won't unless they're 6-year old kids), they don't understand 32-bit computer values simply can't hold much larger values.
If anyone (even scientists) ever managed to store higher values than 2.1 billion in a 32-bit signed integer, 64-bit computers didn't have to be invented.
It's simply a technological limit.
You can either accept it and adjust your money values to fit within the range of -2.1 billion to 2.1 billion, or use some weird-looking, headache-bringing functions to get around it using strings instead of integer variables.
As said before, most people on Earth never reach that amount of money except for the 0,000000235% mentioned above.