The vehicle itself costs 150,000 credits from the store if you are account sharing, but otherwise is free. I upgraded my car to S2 but after attempting this I do not recommend that, even with Traction and Stability control on you can lose control of the car very easily.
My favorite spot is the area right of Yarra Valley Horizon Festival, the road in between two fields. As stated in the other solution, you can use the 'Skill Song' multiplier to make this easier, but as shown I did it without, you will only need 50,000 with a 6.0x multiplier and will take less than 4 minutes to do.
Be very careful when driving through the fields, as the small hills can give you good air and good points on the multiplier, but can also cause you to flip if you are going too fast.
As shown it took an extra 30 seconds for the achievement to pop, so don't be alarmed if it doesn't pop right away.
Video for reference of area and driving through the fields: