Sadly, the book was 50%-off yesterday as their daily deal, but if you sign up with Manning, there will likely be other sale categories that'll include the book (e.g a 50%-off sale on all books-in-progress or whatever). Given that only the first 2 chapters are available at the moment, you might be able to wait for another sale to come round.
But what you will learn even skipping parts, getting frustrated, coming back, leaving again. Is a lot. Knuth crams a lot of knowledge into, well a lot of pages.
Complete disclosure I have honestly haven't completely cover to covered every single volume. I skip around a lot.
http://ocw.mit.edu/ans15436/ZipForEndUsers/6/6-046j-fall-200...
Note: you may still want/need to watch them since there's notation that is likely easier to read off a blackboard vs reading a transcript of someone describing it, e.g.
"The conclusion is the same thing, but summing over all k. So, k equals one to n, alpha_k x_k. Take f of that versus taking the sum of the alphas times the f's. k equals one to n. So, the definition of convexity is exactly that statement, but where n equals two."