Saxson, just a few suggestions. Put the practice book together in paperback form (letter size or larger) with a nice colorful cover (preferably an action shot) and binding. The binding can be done at a local print shop. Make about a dozen copies. Use photos (B&W) and illustrations between the lessons to make it appealing to young players.
A CD with detailed spoken explanations and sound samples (on the sax) would also be a plus and the CD can be attached to the inside of the paperback book by the publisher. The CD can be recorded in a home studio for a reasonable price.
Everything must be original. No photos (without permission) or song samples that still have a copyright.
You can contact well known players to get their written permission to add their photo and a short bio to the book. Students like photos. Perhaps one of the noted players would also write a short "Forward" for the book. Make it interesting for both the potential publisher and the students.
Once a publisher agrees to take it he/she might give an advance of $200-$300 which will be taken off the top of the future royalty checks.
Most music instructional books normally sell for $18.00 to $20.00 and he might get 10% per unit depending on the publisher. The number of pages (288 = 144 actual pages) can be an issue. Some publishers have a contract with a company like Hal Leonard, Inc. that will make the actual copies, binding and the CD from his master recording. HL will then distribute the unit and take a cut of each unit sold then a portion of the profit to the publisher then the publisher sends 10% to the writer once or twice a year.
Some major companies like Hal Leonard, Inc. will not take the book from him but will take it from a publisher who does business with HL and has a good track record on sales. Most large companies have their own staff to produce instrumental books. As such they do not have to pay an outside writer.
Look on the Internet for instrumental music book publishers. For example "Centerstream". He only sells instrumental lesson books of all types;
http://www.centerstream-usa.com/music-books-catalog.php?mcat=Instruments&scat=Guitar
Send a dozen books/CD out at the same time and hope for the best. Mail a copy by certified mail to himself and don't open it. Be ready for a few "Dear John" replies but keep sending the sample book/CD to various publishers.