Undergrad here; not true. I'm currently building a scanner because I hate carrying my textbooks around campus, and any one book is heavier than my laptop. I did search for pre-existing scans, but most of them don't exist. By the way, scanning is only $150+ if you count the cost of a camera. If you already have one for other reasons, or can borrow one, you can make legible copies for free, or spend a little to make a platen and fixed camera mount for better copies in less time.
I'm speaking anecdotally, of course. I've had pretty good luck finding scanned versions of my engineering textbooks, to put onto my iPad. There's only been a couple of obscure or OOP books that haven't been available. It does take some digging, of course. The initial sites were quite open about it, but the publishers have driven it underground onto private sites.