If it is a college textbook, the professor. Textbook prices have more than doubled in the past 15 years but few professors care, or have even noticed. The US has a North Korean textbook market: those who order the things (the professors) get them free, and the ones who buy them (the students) are captive.
The GAO (I simply cannot bring myself to call the Government Accounting Office by its new newspeak moniker) has a report on the college textbook market requested by David Wu (R) Representative from Oregon. Three cheers for him!!! A worthwhile read for faculty and those sent to the poorhouse after buying books.
Still, they fail at the bottom line. Textbooks cost a whole lot less elsewhere because in the US textbooks are specified by the instructor. I can get any chemistry textbook hand delivered complete with slobbering publishers rep the next day at no cost. They will cheerfully pile the supplementary material they carefully designed to kill the used book market (more on that in a later post. GAO has nailed that issue) up to my ceiling.
I exaggerate, but if the General Chem program at Really Large State U, can get slobbering reps and more. The economics are simple. At RLSU the GChem course might have ~5000 students or more. At $140 for the book (more if the students are offered the "package") that is ~ 0.7M$, about 75% of which goes to the publisher and the rest to the bookstore. At our smaller place we are down by an order of magnitude, but the business is steady enough that we can get a decent lunch brought in every couple of years when we consider new texts and all the free copies we want. English and math are the 1000 pound gorillas in the textbook business, but chem ain't bad.
As you might suspect I am a trice uncomfortable about this. The situation is negatively affecting higher education in the US as students seek to escape economic thrall by not buying books, and selling them back as soon as they can. When I graduated I had a library built up across many fields which even today stands me in good stead. To assuage my conscience I don't accept desk copies. If a publisher sends one to me, I call them up and tell them to take it back. If they don't come within a couple of weeks I give it to a student. More later, but you might ask your favorite US academic bloggers what they do about desk copies.