I feel like most hobbies are cheap or free:

- Reading (libraries)

- Exercising (e.g., running, hiking, swimming - depending on pool / beach access -, joining a group of friends who play basketball, etc...)

- Playing video games (e.g., buy Factorio and play if for years)

- Working on personal projects (e.g., writing, coding, etc...)

There are more expensive hobbies, but even then they can often be done cheaply, e.g., though climbing is generally pricey, some gyms are surprisingly cheap, etc...