Every designer earns around the $40.000 per weapon finish in a case. This is the money that is earned by selling keys.

there are ±14 weapon finishes per case so that makes $40.000 * 14 = $560.000

This is 1/3 of the total revenue. Valve takes 2/3 of the split and all the designers get 1/3. This means that
560.000 = 33.3%

(560.000/33.3) * 100 = ± $168 Million dollar per weapon case. Income trough taxes on the marketplace are not included.