Another way to do this would be to crowd fund. Instead of 1 person paying 50$ per book (just a random number, I dunno how much it costs) 10 people can pay 5$ each. 11th person onwards can get it for free.
You could also get some credits from these companies in return for advertising “this book is sponsored by blah company”
You could also get some credits from these companies in return for advertising “this book is sponsored by blah company”