Do you care about the piece of paper? If not, you can likely attend courses in the literal sense—just show up for the lectures—without paying anything at all. Old textbooks are cheap, if you want problem sets, and you almost certainly do—I strongly opine that you cannot learn anything even remotely math-oriented without doing problems. But no rule says you have to do the same problems the others in the class are doing.
Clearly, this is not the method for you if you need a lot of feedback and guidance, nor if you want the credential in addition to the knowledge.
Do you care about the piece of paper? If not, you can likely attend courses in the literal sense—just show up for the lectures—without paying anything at all. Old textbooks are cheap, if you want problem sets, and you almost certainly do—I strongly opine that you cannot learn anything even remotely math-oriented without doing problems. But no rule says you have to do the same problems the others in the class are doing.
Clearly, this is not the method for you if you need a lot of feedback and guidance, nor if you want the credential in addition to the knowledge.