You can audit almost all courses on Coursera, but most of the tests and peer grading is not available unless you pay up. I think they have fee waivers, so that might not be a big problem. The quality of those courses are usually pretty high, made by lots of high quality universities.
https://www.reddit.com/r/udemyfreebies/ has coupon codes to get courses on Udemy for free. The quality is hit or miss, and coupons that are offered might not be what you're looking for, but checking that every day can get you some pretty decent courses.
That's the free part, but building up client contacts and actually working from home is probably the harder part. Bigger places that allow remote work will almost certainly want actual job experience. Ironically it would probably be easier to get hired for remote work if you lived outside the US. I would love to unleash my frustrations with incompetent off-shore workers.