Burning Cars

To get this achievement quickly, end all races prematurely (in career, start a race, then immediately press Esc and end race). You'll quickly reach the end of the season, which'll give you the option to continue.

(In case you want to complete career after getting this achievement) Do NOT actually attempt to continue the game. Like you, the AI gets to keep all items, upgrades and money too, and will make it incredibly difficult to win races since you don't have anything.