A Youtuber who goes by Soushin, uploaded a video showing they grinded all the way to level 99 before fixing the car. Sousin notes the grind took a total of 61 hours to complete.
If you are wondering how Soushin accomplished this, he had to farm for the 25 debased coins necessary for crafting in use of a single fire spell four or five times, while also crafting eight rare coins about three times. After spamming those spells in combat and hunts to gather the necessary money, he would take his party to sleep at The Quayside Cradle for the double experience boost granted after rest. Soushin also ran around to get the material rather than using the car.
You can view highlights from the very end of the grind down below..