These are methods of gaining currency and/or points easily.
1.Farming \/ Farming
Set all Workers to Jump Smash, and hit the box for a while, then leave it for 10-20 minutes, and you will have a big pile of coins. Collect That.
Once you have enough money, set all Workers except for a handful to Uzi or Machine Gun.
Set the rest to Collect.
You will earn money faster than farming.