Well, you can still work out at home. For that matter, if you enjoy dance, this is a great way to get exercise from just watching assorted dance move videos on youtube and practicing them.
In a similar fashion, playing an instrument is just practicing every day.
Do you have an art at all? Have you ever tried drawing or sculpture? Making jewelry? Sewing clothing? Knitting? Wood carving? Carpentry? Crafts make good hobbies and you learn some useful skills along the way. They don't usually cost much and can be self taught. Also, if you get good at them, you can often sell your projects online. Such crafts are often cheap to start, even if avid crafters can spend a lot on such things. Something like quilting is just using scraps to make new garments or blankets.
For that matter, do you know how to cook? That is a cheap hobby, because you can save money doing it, as processed foods always cost more. You're going to eat a lot of meals in your life, so why not learn to make them cheap and healthy? Also as a bonus, any adult is a bit blown away when they come home and their child has already done what they see as a daily chore.
Do you have a local PBS station? A lot of their programming, especially if they have multiple broadcast channels are craft shows.
Then there are hobbies which can turn into careers. Have you ever tried to learn how to code? Obviously, you already have a computer, so why not learn how to make it work? Or you could take up writing, even when you're not doing it for school work.
You have the time, why not try a bit of everything and see what you find to be fun?
There are low costs ways to try a lot of things, if you bother to search them out and are willing to experiment. You don't need a kit or expensive materials..