By teaching yourself.
I agree, but that's actually difficult for me. This is going to sound silly, but no one ever taught me how to do that. I'm also bad at teaching myself to teach myself.
This is probably the most interesting post in the thread to me - I think it gets to the core of the problem. And it sounds like a great challenge to tackle because it's such a huge step in self-sufficiency.
I would pick one thing you want to learn and brainstorm how you could learn it without paying to take a class on it. On a ridiculously tiny level, let's say you've never made a smoothie before, without taking a cooking class, what are two ways you could figure out how to do it?
That's pretty easy, but take that thought process, and apply it to the next thing you want to learn.
And when you are teaching, whenever possible, ask your students to do that as well. For example, if you are teaching ESL, ask them: Outside of class, what are some ways you could improve your English skills? See how many things they can come up with. It's a great exercise for them (teaching them to teach themselves) and also you see how many of the ideas they come up with can also be useful for you if you are trying to master another language.
Languages--without taking a class, I could get a textbook, look up a syllabus online (for pacing information), and advertise on Craigslist for a language exchange partner. I could also Google YouTube videos, possibly the news, with captions or accompanying transcripts in that language. I could also, with the help Google Translate, keep a journal in that language with information about my progress. I could also sign up and practice my pronunciation on free sites like Duo Lingo and Live Mocha. It would be a little slow at first, but after a while I might catch on and start being able to have decent conversations in my new language. Now, all I need is a conversation partner and a decent textbook.
Math--I could practice basic math on Khan Academy, take a look at the course requirements for a teaching certificate in math, purchase a textbook from Amazon, work through the problems and check the answers in the back of the book, use Google to look up real-world examples of the problems, and find sample Praxis math tests. I could also hire a tutor to work with me on studying for the math Praxis.
Science--Again, it would be beneficial to look online for a list of course requirements, buy or rent the textbooks, download a syllabus outlining what I need to study, watch videos outlining the subjects, Google practice Praxis tests, buy a Praxis test prep book, and hire a science major as a tutor if I'm not sure of myself.
Computer Programming--my best bet, I think, would be to approach it as I've approached the other tasks above, except I think I need to find an apprenticeship in the area to really feel confident I know what I'm doing.