Think of it like this: your fee credibility is as important as putting on your clothes before going to a speaking engagement. Having questionable integrity when it comes to your fee, will leave you open for attack from many different angles (as would giving a speech nude). Without question, all hiring events should receive identical fee bills, as long as they are getting identical presentations. Overcharging or undercharging an event will do nothing but get you in trouble with the speakers bureaus and ruin your good name.
Having a product in your package allows you to negotiate your fee a great deal more than otherwise. For example, if someone asks you to speak and tells you that their budget can only afford to pay $7000.00, but your fee is $8,500.00; you must rework the situation. Mention that your fee includes 100 copies of your book, but you will take them out of the deal. I have pulled books out of the deal and have still been allowed to sell them at the back of the room at many engagements. This is a legitimate way to maintain your fee credibility without shorting yourself or the hiring event. Remember that not playing fair will only hurt you in the long run. Above all else: make it work so that you keep your good name, and the job.