Source for WLS Regression

#1
I'm working on a paper in which I run a study using a WLS regression methodology. I understand conceptually how it works and can run it easily in R. However, the statistics textbook that I have has only a very brief paragraph on the subject, and I need something with more detail to cite in my paper to explain why I chose the methodology I did and how it works.

Is there a statistics book (that's not a $150 textbook) that anyone is aware of that has a good detailed description of WLS regression, how the math works, when to use it, etc? I've searched and it seems like while most statistics books mention WLS as an alternative to OLS, they don't go into enough detail for my purposes.

Thanks!