My original Millionaire's Club video from over 10 years ago from the original Burnout Paradise!
The following video and solution is intended to help people who are struggling with getting 1,000,000 points in a Stunt Run for the achievement. Basically, follow these steps and you should be able to get the achievement with enough practice. First of all, know that the time limit doesn't really matter. Just stay in one combo and when it says Final Run and the timer is at zero, you can keep your combo going infinitely (as long as you do stunts and don't crash). Also, any stunt car should be fine for this achievement so that's mainly up to your preference.
Stunts to keep your combo going are as follows: Boosting, Drifting, E-Braking, Air Time, Billboards, Super Jumps, Flat Spins, Barrel Rolls, Reverse Driving. Just make sure your circle doesn't become fully red because that means your combo is just about over and your whole stunt run will end too. Anyway, get to the location on the map where I am at and start the Stunt Run called "Express Yourself".
Try not to use the same ramp you used before because it will say Stunt Failed and you won't receive credit for points on that jump, so use variety. Also, while I did a barrel roll in the video, it is very risky so try sticking to flatspins only when jumping off ramps. In the video I get 2.6 million just to show more possible stunts in a good line if you can't make some of the other jumps. There are many good stunt opportunities in a row here. Anyway, good luck and once again, just boost or drift every so often to make the combo timer reset so the combo doesn't end.