Million Dollar GranddadG 25

For fully upgrading your kart. You should have most of it done by the end of your second career run. Quickest way to finish up is to start another career, and keep rerunning the first race. Just hit retry at the end, and keep building up money. You can check how much you need in the Garage before you start, so you know when to continue and finish upgrading in the menu screen before the next race.