Depends where you want to compete.
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.