Initially, I was pricing these PER REVIEW (at 25¢ each), which seemed to be an equitable solution ... but I've had feedback (notably from some folks who want to SELL them) that this is confusing (as the book length and pricing diverged depending on the length of the reviews), and that I should go with a "flat rate" per volume.
Now, I had other feedback, early on, that was suggesting VERY low cover prices. However, as these are coming out from CreateSpace, I need to have the cover price high enough to be able to at least have a slim margin on their "expanded distribution", or I can't get the books out into those channels. While I've not run the numbers for all the existing books (which I recently re-did to add in the by-author and by-title indexes), I'm pretty sure I'll be OK with that, even though this will be (excepting the two shorter books from 2014 and 2013) an across-the board price reduction.
The idea of going with a flat rate started to make sense when I got into the middle of working on the 2009 book (soon to come), which, featuring 81 reviews, would have been priced at $20.25 at the per-review rate ... which seemed to be a bit steep for a 220-page book (and quite a bit more than than some of the other longer, but with fewer entries, volumes).
Being a bit of a contrarian, I couldn't JUST pick a round number out of a hat, but decided to try to find a "special" number, and opted to get a listing of prime numbers between 1499 and 1699 (there being 28 numbers in that range). Unfortunately, I couldn't get anybody to go over that list and say "oh, that's a GOOD one", so I was pretty much left to my own devices.
And, frankly, there's not much out there (or at least that I could find, my Google-Fu may have been wanting on this) for simply analyzing numbers that aren't names or birthdates, etc., short of reducing them to one number and getting a vague blithering about that (although, I guess if your market is China, it would be good to have that reduce to an "8").
In terms of a "price", I was favoring one of these, 1597 ($15.97), which was less than I had been charging for most of these, but enough to cover the XD nut with CreateSpace ... and, while trying to find some resource for analyzing these numbers, ran across the info that it's part of the Fibonacci sequence ... which sort of sealed it for me, as it's a "special" number, if not necessarily related to selling books!
I am thinking that maybe I'll end up combining the 2014 and 2013 books (which are currently $10.00 and $10.75 respectively) into one volume which will end up being right about the same length (/cost/margins) as the 2015 edition, at that would be a pretty big price jump for fairly slim volumes.
Anyway, I'm SURE you were waiting with bated breath for more news about the review books ... you were, weren't you???