I hesitate to call this an answer, since it is based on no actual experience, but I would make three points:

(1) It is not clear to me that you have no use for a publisher. Publishers work to promote your book to libraries, book stores and to faculty looking for a textbook. They also may be willing to pay you an advance on your future royalties, which would opportunity risk of missing other forms of income by writing a textbook. I also would not assume that book publishers would not provide useful editing if you wanted it. You might be interested in Cory Doctorow's thoughts on the benefits of working with traditional publishers. Doctorow is a fiction writer and essayist who distributes all of his work under a very permissive CC license. Fiction isn't textbooks, of course, but I think there are some interesting ideas here.

(2) If your goal is to print copies of a PDF file with no professional editing, Lulu has a good reputation for that sort of thing. I have no personal experience with them, and the people I do know who have experience were printing fiction and prose, not math, so take that for what it is worth.

(3) The obvious person for you to talk to Allen Hatcher. His Algebraic Topology textbook is freely available for download, but is also sold in hard copy by Cambridge University Press (and is very good!).