DRM business costs

I represent a business that retails bundled eBooks from various publishers. Some of these will require DRM encoding to be added to their product. It's impossible to make a bundle model work if you are retailing a package of 20+ books with an additional download cost for each book and each format. Is there any business plan that will allow a download cost to be applied to a bundle of product (our retail product) rather than every individual book in that product?