Shutterfly will bind 100 pages. The problem with breaking mine into 1/4s is you are paying such a high setup fee. The base price for an 8X8 is what, $29.99 + $1.00 each add'l page? If you print 26 or 27 pages, that's $38 (give or take) for the book, plus shipping. $38 X 4 = $160 (give or take).
Two 52-page books would be $29.99 + $32 each, or $64 (give or take). Twice that would be $128 (plus shipping). This is REALLY rough math.
So you come out ahead doing as few as you can, because you're knocking off the $29.99 setup fee.
For what it's worth!