Capo - 300,000
Boss - 2,000,000
God - 4,000,000
You can view your rank from the leaderboards or while you are in the main menu to the bottom left it will show your score, next to the star.
Getting to God rank will take you some hours and a lot of grinding, but its easy grinding and can be done alone with a guest account signed in.
This method should take you roughly 1-2 minutes, including loading time.
Create a private match and have a guest sign in. Before starting the game, press to change the match settings. Also, having the speed perk on your character helps out. Select the following settings:
Choose map - Skyscraper
Number of bots - 0
Bot Difficulty - Noob
Set goal - $9000
Costume weapon set - Earthquake (ONLY)
Start the match. Now simply walk over the earthquake power-ups and press to use it (you do not have to be close to the enemy to affect him). Wait until the enemy stands back up to hit him again with another earthquake power-up.
Now there is a small trick to give you and extra $400 at the end of each match. To do this simply walk of the edge of the skyscraper ONCE after inflicting damage to the enemy, this will make you lose $100. Now continue using the earthquake power-ups until the match is over. Rinse and repeat this over and over.