Book cover with RFID-tagged zones?

I would look at using LF or 125KHz tags, and very small "button" tags like these would work great. Also, I would choose a very low power reader with very short range. Something like the ID-12 might work perfectly for this project. If you have some electronics experience or have an engineer on your team, the ID-2 might work really well, but you need to build your own antenna loop coil.

For the reader/sound emitting portion, you could do a couple things. If you need it to be totally stand-alone (with no PC or other hardware), you can bundle together an RFID reader, a microprocessor, and a sound recording chip that lets you play various sounds back based on I/O pin controls. If a PC or laptop or netbook can be involved, then you can get some additional parts together to connect the ID-12 reader to the PC over USB and use software on the computer to read the book IDs and play sounds back.

If you are planning on making more than on of these books, then you may have to use another type of tag because your basic LF "EM4102" based 125KHz tags will all have unique tag IDs that you cannot change, so you will want a tag that is programmable so "zone 1" on every book has the same tag ID.

Ahh well, it appears you are more versed than you originally let on :) When posting questions, it's important to explain the full capability of your dev team and  the scope of the project (mass market or one-off), as that will determine the type of advice given. Be sure to fully explain things like; Do you need to play monotone sounds or do you need to play music or a recording of some kind? These types of details are affect the type of advice you'll get.

As for pricing, you can get RFID labels for $0.10 and even $0.01 if you buy in large enough quantities... but again, if you are doing a one-off project you will not find these prices hold true for you.

Overall though it sounds like you are planning on mass marketing this and you already have enough of a head start identifying the tech needed to make it happen, so is there any more detail about your project you can give us or any specific questions you might still have?