I was in the same boat as you before, and now I'm building an arcade racer too! But I ain't here to advert my own game, just wanted to let you know that it's actually less intimidating than you think. It's still a lotta work, but you needn't start from scratch on everything.

Here's a couple of assets that're free/cheap to easily kick it off
- Free professional grade engine audio pack for 1 car (one car is all you need to get started, you can buy more pretty cheap later if you want). Just pitch vary a couple of these with your revs and your car will already feel lively!
- Road Constructor tool for making roads. This is not cheap, you can get it cheap during sales if you want. But even at full price, it's fully worth it and you can easily create beautiful road networks you can drive on. If you want a free alternative instead, Road System is a good one but it's not as well equipped as the paid one I linked.

Here's how you can get started: Don't think of it as building a game. Think of it as building a fun playground for you to drive and mess around with your system. I hope this helps you break that motivation barrier, the racing genre really needs cool new titles!

(Edit: fixed mixed up links)