This is not a 100% guide but I found a way to make money pretty simple. First things first is you are going to have to play the game normally to unlock the bikes so you can buy them. But here is the trick you can press start and go pick missions and what you are gonna want to do is select escape and doesn't matter which one you pick just press one and when it counts down from 3 press start as soon as it starts and you just keep it paused for 30 seconds and boom it will say mission passed. Just keep doing it and you should have the money soon some missions pay out more so mess around with them hope this helps.