IT is a bit overwhelming, but it's not that complicated when you start revving. :)
At the moment you can get keys for 2020 season - either on secondary market/opensea/private sale or wait for the main sale. Prices are listed in the post. But competition will not start until late January.
To start racing (tier D/C) in 2019 season, at the moment you need about 0.5-1eth to get a car/driver/set of tyres and some parts - depends on your efforts to find/assemble cars.
I usually have several bundles on opensea for either tier D (~6000 points) or just the essential kit for racing car/driver/tyre but you can buy all parts separately as well - but it takes some time to get a grasp on what you want and need.