Hi everyone, this achievement can glitch, but it doesn't have to be.
If this achievement does not come, you have to play the campaign again in the new game. You can buy your way through to the Chevycopter, after which you should bring the Alman-o-tronic so far that you unlock the quadrotor. With it you play through the whole campaign until you have unlocked the master key. Now it is best to play the Mars map and when you have completed it you can buy the Cool Bus and the Scrapolice Helicopter. That was my way to unlock the achievement.
Good Luck everybody. :)