My Control Theory I Professor just saved me $160.00. There's a required textbook for the course but he told the class no one has to buy it. That if we do, it won't be a waste because he'll be using it in Control Theory II as will another professor.
You see, he originally started teaching when the 3rd edition of this book was out. So he crafted his lectures around that book. Now, X years later (or maybe six months in the textbook industry) the 6th edition is out and he doesn't feel we need to run out and buy new editions just because some editor changed a few things. Maybe because the 5th edition is so hard to get ahold of. He's said the course is "self contained" and we'll get all we need to know from lectures. We can use the book if we want, but don't have to. This year even he'll be writing his own homework problems for the class instead of using those from the book. Double advantage to me, the person who never has solutions and/or friends which should keep all the cheaters from automatically getting a full homework percentage. It's always nice when a professor respects your budget as much as you do and does what they can to save you money, even if it means a little extra work on their part.