All the money you will need!
Once you have gotten a mission that sends you to the islands, stay there and get money. There are prirates that sail the seas that way, they will rob you and take all your stuff. But be quick and rob them first. They respawn in different places, grab a boat, and go fishing!
P.s. I spent one hour working this methoid, & got 80 million in cash and 28 keys.
I own most of the investments now. Buy the most expensive first, and then next most expensive and so on. Money will flow into your hands quicker
Added by: criegnice Jan 23rd 2008, ID#28973