In short; money is really tight at the moment and need to save up for university. I'm a 17 year old student who have just finished basic multivariable calculus and differential equations.
I was wondering if you could recommend some free or very very cheap books, which have a reasonable standard. I'm mostly aiming for books covering either of these, but feel free to add others as well: Linear Algebra, Real/Complex analysis, Logic, (number theory, topology).
I am aware that free/gratis content might not be the best, and can be full of errors, but it's better than nothing, right?