The best way to get this is to play the game all the way through, buy all of the constructs as they come up. Then replay the last level all the way up to the boss on the easiest difficulty. Spam the jet as fast as possible and be sure to use your LB+RB power up right when the big robot comes up on the 2nd part of the broken highway. Once you start to fight the boss just quit out, rinse and repeat.You can average around 6-9k every 5 min or so. Much faster than just replaying levels again.