No one is more sensitive to the ever growing cost of textbooks than students. And it may surprise students to know that faculty are also pained by publishers selling the 8th edition of a book for $200. While we are happy when publishers offer great books and make money from that effort, something probably needs to change in this model. Here is a list of “free” books approved by the American Institute of Mathematics. Note this is free as in beer, not free as in freedom (what is the distinction? You can find that here)
In particular, note the multiple Calculus and ODE offerings. If nothing else you can use these as references or as sources of problems for further study.