Stock trading robots - you won’t make much, but you can dip a toe in the water... After/if you figure it out, you can scale easily pretty much up to millions and more...
For starting here is my advice: get a small linux VPS or just install python on your laptop, get as much back data as possible, covering at least one market cycle (this will be your initial expense) and start back testing every trading strategy you can find on the net or in books (library) for free...
Never pay for strategies, because they will all fail, but by testing them one by one you'll come up with your own ideas and one day hopefully you'll find your edge...
It's not going to be easy or "get rich quick thingy", but it is well worth it in the end...
Use historical pricing data, NLP and comment volume on cryptocurrency subreddits and threads, frequency of search terms from Google analytics, major exchange status (Coinbase, Gemini, Kraken, etc. - whether they are up or down as dummy variables), frequency of crypto-related news, etc. all plugged in as features into models in Python and linked with Gemini trading API.
I started working on it and then got lazy (and bad RSI from being at my computer way too much) and it never materialized. Plus, I guarantee somebody else is doing it, or models like that probably aren't too successful anyway.
Could be fun though.
You need money to make money in this world... But if you have an edge, raising money won't be a major problem...