I have neither been in similar situation nor do I have any experience in the field. I am a CS student and often visit related subreddits, these are the info I can share:

Every few days someone posts on https://www.reddit.com/r/cscareerquestions/ about applying to 200 jobs to get one interview which includes people with degrees, projects and internships. Even in median cases, it's still competitive. Going to low-cost college for CS/CE will give you enough info to know if you are interested - and getting a degree will make getting a job much much easier. Degree or not, process of learning enough to be able to get interviews will be in years, my guesstimation would be from 1.5 to 4 years.

Where do I start?

No clue, depends on what you are trying to do and how general/focused you want your study to be for that.

How can I develop an interest?

Dual boot/use virtual box with a linux OS, try to use terminal for as many things as you can. Learn about Unix philosophy, learn to use common unix tools. Learn about famous people in C, living ones like Richard Stallman and Linus Torvalds can be interesting. Watch talks, like from this guy: Maciej Cegłowski or from defcon etc.

What free resources are the best?

No clue, depends on what you are trying to do and how general/focused you want your study to be for that. College being a good general option.

What language should I learn for the best hope of contributing to the marketplace?

Finance professionals gather up all sorts of information, model it and do calculations to try and evaluate which would be good investment. Their primary motivation is also money. Do something similar to figure what you should learn.