This is a relevant article on the Clark Howard website:
It depends on how good your safe is, how handy your guns are and how much ammunition you have.
I think that is a reasonable number… but in our case, we pay several individual Service Providers in cash and can forecast it.
Frequently, I go to the bank for $600… 20x$20, 15x10 and 10x5.
Easy to remember and works.