If you don't have the authority to change the textbook on your own, at least for your own section, then your target should be, not the publisher, but the person or committee that does have that happy power.*
Show them this: http://aimath.org/textbooks/approved-textbooks/ and propose that you teach a section of your course using the appropriate open access textbook. (Edited to add: Pick out the appropriate book and an alternate before you talk to the committee or coordinator and be prepared to defend your choice vs. the approved text.) In the following semester, compare how well your students did in the next course in sequence vs. those who used the standard text.
Your secret weapon: work like hell to be sure your students are well prepared for the next course.
In the comments, Ben Crowell has said: "Here is a catalog I maintain of free books, including many open-source textbooks: http://theassayer.org" I've edited it into my answer so it doesn't get lost. Thank you, Ben.
* Hat tip to Professor Severus Snape for "happy power."