I graduated four years ago, and am currently in grad school.
As an undergraduate at a small private college, I can only recall two professors who required their own books. One was a paperback physics reader for a very large class, available from the department for $20 (or from upperclassmen for less). The other was for a small math class, was not unreasonably expensive, but also was not very good, but when the professor left halfway through the semester with health problems, the department bought us all copies of the new book. My professors were always accommodating to anyone who wanted to buy an older edition, and in one case explicitly told us not to buy the expensive new edition.
In my current department at a large public university, I know of only one professor who requires his own book. It's about $40 and has only had one edition since it was published 15 years ago. In most lower division classes we use an in-house online homework system, although we don't have a good database of problems for differential equations, so we've typically required the latest edition of Boyce and DiPrima so students can use the publisher's homework system. But we've started work on our own problem sets, and we are at the point where we can use our own in-house homework system for it, if the professor is willing to put in a bit more effort organizing and debugging homework.
Anyway, this sort of exploitation is not typical in my experience.
As an undergraduate at a small private college, I can only recall two professors who required their own books. One was a paperback physics reader for a very large class, available from the department for $20 (or from upperclassmen for less). The other was for a small math class, was not unreasonably expensive, but also was not very good, but when the professor left halfway through the semester with health problems, the department bought us all copies of the new book. My professors were always accommodating to anyone who wanted to buy an older edition, and in one case explicitly told us not to buy the expensive new edition.
In my current department at a large public university, I know of only one professor who requires his own book. It's about $40 and has only had one edition since it was published 15 years ago. In most lower division classes we use an in-house online homework system, although we don't have a good database of problems for differential equations, so we've typically required the latest edition of Boyce and DiPrima so students can use the publisher's homework system. But we've started work on our own problem sets, and we are at the point where we can use our own in-house homework system for it, if the professor is willing to put in a bit more effort organizing and debugging homework.
Anyway, this sort of exploitation is not typical in my experience.