Hi, I have been getting questions from people on Xbox about this achievement so I will put this guide up for it.
I got this achievement halfway through season 9.
Here's what I did, I played and won the first 3 seasons for the achievements attached to them, and then simulated every race from seasons 4 onwards in the Sprintcar category as it has 35 races per season and thus making you the most money, with one exception as I did race & win the last race as its a showcase race which nets you $150k-$160k.
Yes you can spend the money on upgrades/repairs as you only need to make $5 million not bank which people are worried about. The achievement popped for me when I had around the $3 million mark.
Good luck with it.