Pole-Vaults! They are amazing! Even if you don't get the height needed for a Back-flip you can Handstand/Superman into Pole-Vault/Up-and-Out Combos. These type of jumps can easily get you money, and the hard badge is very easy to get when doing this. I think it's a lot simpler than doing tons of tricks mid-air personally.
Once you have the Gold Cart, Twirly Hat, Upgraded Wheels, Upgraded Rockets, Up-And-Out, Handstand/Superman, Bat and Pole-Vault, you can easily make 40k a jump, that's with a cart full of groupies though. When the groupies die, they're only 20k to replace though.
When jumping with all of the previously mentioned Upgrades/Items, get a nice jump off the ramp, immediately go into a Superman/Handstand while doing a back-flip, get in an Up-And-Out if you can to set a higher Combo, level out, and right upon hitting the ground do a Pole-Vault, and get in a few Up-And-Outs, and every time you are about to hit the ground do another Pole-Vault and immediately do a Up-And-Out and level out, and repeat until you stop.
Have to finish in 1:12:00... Okay, lets do this... Alright, a quarter of the track left, only 15 seconds remain, BOOST > POWER-UP!! > ALL CARS ARE RED > INFINITE BOOST > WIN!!!!
I had a jade Z a brass T and a brass G as well as an iron T and an iron E and I threw in Zeitgeist, hell of a way to get that achievment, lol, 256 damage or so I believe XD
 "Neverending Light"){kind=icon}
 "UpBot Goes Up"){kind=icon}
 "Shopping Cart Hero 2"){kind=icon}
 "Necronator 2"){kind=icon}
 "Feed the King"){kind=icon}
 "Accelerator"){kind=icon}
 "Treasure of Cutlass Reef"){kind=icon}
 "Pirates Vs Ninjas"){kind=icon}
 "Neon Race"){kind=icon}
 "The Tickler"){kind=icon}
 "Clockwords: Prelude"){kind=icon}
Thank you :)