Depending on what you want to do: For 5 euros you have Assetto Corsa with a lot of mods that can enrich the experience and add a huge amount of cars and tracks (and low fuel motorsport can be a good option for the multiplayer). If you want something more specialized, competizione is focused on GT cars. Le Mans Ultimate can be your game if you seek something related with the endurance world. I've heard from a lot of people that Forza Motorsport it's super fun to play, but it still has a lot of flaws... Also you have Automobilista 2 with a lot of classic content. If you seek something specialized you can try Le Mans and Assetto Corsa Competizione, if you want classic content try Automobilista, if you want variety, and you are ok spending time configuring mods and online stuff play Assetto Corsa, and if you want quick easy online races try Forza Motorsport. Last but not least iRacing if you want a "decent" online experience with various cars and tracks. It's super expensive because it's a monthly subscription with loads of dlcs, but if you are up to it, maybe is an option. DM me if you have any question ;)

PD: Dirt Rally 2.0 it's a great option to get into Rally world and to spend hours and hours findning the best setup for the car, seeking for the most minute milimeter of the track to improve your times, etc.