Sometimes, when you're trapped between multiple bad options, your only solution is to take a third path. Get a little creative in how you approach things.
Writing: I write fan fiction. Makes the subject matter easy. Or easier, at least. While you can't charge for it, what you can do is set up a Patreon which lets people donate in order to support your work. If you don't want to write fan fiction but can't come up with your own subject matter, take writing prompts from other people(you can get paid to do this, I hear?) or throw dice on a list of random words.
Money: You would be amazed at how much money you can make by walking dogs. Walk a dog for an hour, take 10 dollars for it. The thing is, you can walk multiple dogs at once. If you can walk 4 dogs at once, that's 40 dollars an hour. This is broken.
I don't have the money for classes and textbooks. They'd probably learn quickly I'm just a worthless fraud anyway. Just like my previous jobs.
I just want to give up.
Part of how you live your life is influenced by how you see yourself. If you think you're a worthless fraud, you might end up acting like one. So don't. Consider the good things about yourself. Don't give up. If you have to, try self-hypnosis or other mind shenanigans to restructure your thinking.
Therapy: If your mental state is problematic, therapy would definitely be helpful, but if money makes that an issue... but like I said, you can get creative. The essence of therapy is talking to someone trustworthy. Find a priest, maybe. Even if you're not religious I imagine a good priest would still be quite willing to talk to you. I'm also sure that many of us on Bay 12 would also be willing to talk to you in private, though this may be a little iffier.
Learning:
This is incredibly dangerous advice. Humans are notoriously full of shit, and when trying to learn a new subject without the guidance of a credentialed expert in the field to guide you away from seductive bullshit and to call you out on your own shit, you're very likely to fall victim to any of the numerous cognitive biases that we all have to wrestle with when trying to make sense of the world.
Trying to learn completely by yourself can be tricky, yes. Which is why you find hobbyist groups, free online courses(Coursera, anyone?) and the like to help you out.
Overall: Don't give up. If you have an issue that the standard approach won't fix, find an unusual approach. Get creative in facing your obstacles. If something doesn't work, ask how else can you fix this? While circumstances may impact you, ultimately
you are the greatest factor of your life.
Grandmother's junk:
Give it a shot. A lot of how much we consider stuff worth can be adjusted. Perception of an object, for starters, can be adjusted(take better photos). A little cleaning and whatnot can also help drive something up. Flipping can work.