devtrackers.gg
I'm surprised the solution isn't a new currency that's worth 1k gold. 1000x cash limit and looks a lot cleaner than all of the gear being worth "billions"
At this point, runescape coins are the equivalent of pennies. Maybe even 1/10th of a penny.
That's basically how it works behind the scenes, but the new coin is worth 1B rather than 1K. (This new "coin" isn't a player accessible item though.)