If [i]literally just multiplying by twenty[/i] is terrible and complicated for you, I'm sorry.

The ratio is arbitrary because it can afford to be. It's simple and it's realistic, and I don't want the in-game currency to be a lame ripoff of the dollar or pound that most English writers are used to.

If you'd rather write a fictional world whose subtle details are actually just a copy of what you see every day, suit yourself.