I agree - some of the textbooks on there are extortionately priced. I did put some free resources at the bottom of the article, although admittedly I could hav

I agree - some of the textbooks on there are extortionately priced. I did put some free resources at the bottom of the article, although admittedly I could have added more. If you look at the link in the first comment there are some great lectures in there. Leonard Susskind's Stanford Modern Physics lectures are fantastic. If you search on YouTube for Stanford/Susskind/General Relativity etc, you should be able to dig them out.