You can ask your printer to produce pages with full-color images or graphs on a color laser printer and collate those pages into the document before it's bound. That method will give you color images at an affordable price. Customize content as much as possible. Each training manual should contain materials specific to the topic or employees' responsibilities. Modern network printing options make it possible to generate high-quality materials in extremely small quantities.
Desktop computers make it fast and easy to cut and paste content electronically.
There's no reason to issue a 150-page manual when only 50 pages pertain to the subject. Any additional cost from customization can be at least partially offset by reducing the total volume. In the case of training materials, bigger is not better. Put the recipient's name on the cover. Nothing impresses an attendee more than seeing his or her name on the cover of a manual or booklet.