I don't believe there is an extra fee at renewal or issue of the larger book, they just use the bigger book so the amount of work on their side is the same. If you add them in later you will have to pay.

I have seen more than a few people who have asked for the larger book and were sent the smaller one though.

There is also an option now to issue 52 additional pages instead of 26, so that will cut the cost down if you need to add pages twice.