The stunts are amazingly easy, because as long as you boost every 5 seconds you can keep it going.
My technique is that wherever you are, head up to the northern train tracks. There's five ramps in a row right there that earned me a million points (at least) every time.
Well the stunt RUNS anyway, we were speaking mainly of the barrel rolls of course, which are obviously the hardest stunts. They're the only ones they put a 2+ multiplier on and you can easily wipe out and stop your run on them, thus too risky to be reliable.
1 million is very good, I haven't gotten anywhere near that yet, though admittedly I have not learned the map well enough or focused on stunt runs enough to perfect them. I had a lot of fun last night though beating one of the NW stunt runs that requires 170,000 using the Hunter Takedown 4x4. There's a spot up there where you can link many Superjumps and Billboards, and a high drop to the train bridge via offroad shortcuts.
The Takedown 4x4 is hard to handle, and rolls over small guardrails easily into non playable crash areas, so you have to be careful. It is very durable though and resists vehicle crashing well. I captured a video beating that run with it getting 262,000, but since it ended shortly after getting on the train bridge due to letting the 5 sec timer lapse, I scrapped it. I suppose one could get a mill even with a rig like that considering how many Superjumps and Billboards there are once you get onto that train bridge.
I do have a couple videos I captured using the Hunter Racing Oval Champ though. It's one hot car, a sort of combo Speed/Aggression vehicle in the Aggression class. It's basically a sleek modern looking stock car. I actually collected it by accident on my way to record another stunt run with the Takedown 4x4. I saw it stopped spinning it's wheels after smacking headlong into a bridge pylon.
The Takedown 4x4 is very fun to race with. It's a lot like playing GRID with the Repulsor Field cheat on. Cars go flying off it. LOL I effectively beat the game last night, as the credits roll once you obtain a certain license level. There is still much game to play and a higher license to achieve though.