Formula 1 is unfortunately the best place to start because it's the most readily available (legally) and is like $60/year which is fine. I think it's a good place to start because frankly it's lacking the nuance that makes other disciplines more interesting but has enough there to at least be immediately entertaining. Every driver and team principal is a celebrity of sorts, so there's a lot of egos clashing that makes things interesting when the races inevitably become kind of boring/predictable. Its broadcast (commentary and overlay) is also still a cut well above the rest of other motorsport which helps new viewers get engaged with that's going on. If you have Netflix, I'd recommend watching the latest Drive to Survive season to get a primer on the drivers/teams and what makes the drama of it so interesting. Though I'd add the caveat that a lot in that series is contrived/forced. Still entertaining, at least!
If you're in Aus/NZ, I recommend watching Supercars (formerly known as V8 Supercars). It's contact racing in city streets and is thrilling, and pretty easy to watch if you're around there! I think? It's on TV. If not, it's $20 USD per year which is crazy cheap for a lot of great racing action.
If you like motorcycles, MotoGP costs like $250/year which is insane and stupid and I don't recommend it unless you're really devoted to it. You're better off pirating it. Either way it's maybe the best motorsport around. Constant close competition. I don't think it's as easy to get into, though, since the overlays aren't as good and there's an inherent knowledge of racing you need to understand to get the most out of it. Things like tyre wear, drafting, teamwork, etc. The commentary tries they're best but frankly there's so much going on every race that they don't get a lot of time to explain the basics.
NASCAR is also a thing and I like it a lot but it's hard to recommend as a "get a lot out of it" sport because you really need to understand racing strategy and the specific things that make NASCAR interesting to watch all 3-4 hours of it every Sunday. If you're in the US, though, it's readily available and if you're outside the US, I believe they upload full replays on YouTube. At least, they used to when I lived in Japan.
I love watching racing but none of them justify the asking price right now. Every motorsport is full of rich people making shitty decisions, take their shit for free.
I will also add, that you don't need to watch new races. You can watch old races! There's so much old shit to watch, and you don't have to wait for the 6 week summer break before the next race! There's so much to watch, you can go through 20 seasons and start back over at the beginning because you've forgot shit! It's great!
Also MotoGP was more like $140 a year or whatever but they're on my shitlist right now, Dorna's commentary is god awful
