I am currently taking a GR course and I am finding the following quite useful:
Ruslan Sharipov's Website has some GR relevant material, specifically books number 3,4, and 6. These books are
free, as you will see is stated within the first few pages of the book.
Also, Sean Carroll's GR notes
are freely available online too. Arxiv material is legitimately free. I am not sure if these notes are the same as Carroll's book Spacetime and Geometry: An Introduction to General Relativity
, but I doubt it since the free notes are 231 pages long and the book is more than twice as long.