I teach mathematics at a community college. The content I cover has a very slow rate of change. There is no valid educational reason for textbooks to cost so much in my area or to change from year to year. I decided some years ago stop using paid materials on my courses.

I create most of the content myself. I have my own problem sets with solutions and create almost all of my own lectures. It was a lot of work to get everything to the point of being able to stop using paid materials but the up front work pays dividends in making my job a lot easier now.

I don’t know how feasible this is for other areas but in mathematics it is. The problem with open textbooks that I’ve seen is that they tend not to be done well. I’ve found a few open textbooks in math that are very well done. The nice thing is that when you find one that is done well you won’t ever have change books.