It should be fairly easy. You just need some tracks, things that are in the races (whether cars, humans, or some imaginary character), set up the racing system code (about 300 lines for the core components for the very base fundamentals, more for additional players). For other features like upgrades, track selection, etc., that'll take a little more effort and time to do. I suggest starting with a single, simple track and get the basic core components down. Then, when ready, make a bigger track to about how your game will have it.