If you want easy money go to the industrial estate, around near the prison, where you help Gerry with his "I'll Take Her" mission.

You will see a light green and tanned grey van that has group 6 written on it. That is the money van.

Blow it up and then lose your wanted level with a cheat because the police will be on you.

Then go to were the van was blown up and you will see at least 30 money piles...