The ideal way to package to keep the cost down is not the same as the ideal way to package for use.  Except when the book is so large (too large) that it blows out the possibility of using standard bindings, one book is cheapest way to package.  The ideal in play is a bunch of separate booklets, none of them terribly big or heavy, that you buy in a boxed set.  Then you can pass around different parts of the game to different players as questions arise.  This is not cheap.  So a 3 book set compromise is not the worst thing in the world.

The real problem is bloat.  Or sometimes replacing useful content with bloat so as to turn 3 books into 3+N books, or in worst cases, never getting around to writing the useful content no matter how many books are provided.  My ideal compromise format is 1 player book and 1 GM book, so that players don't need to purchase all the GM stuff. 

Those booklets are so nice in play, though.  Especially when you make strategic use of the back cover, and the first and last pages. 

Quote from: MeganovaStella on January 16, 2023, 06:42:13 PM
there should only be two initial books:

1. mechanics, 200 pages at most

2. lore, can be up to 1000 pages detailing how everything works in the setting

2 books, is plenty; in my opinion.
Book #1. Player Stuff
Book #2. DM / GM Stuff

Quote from: Jam The MF on January 16, 2023, 10:42:29 PM

Quote from: MeganovaStella on January 16, 2023, 06:42:13 PM
there should only be two initial books:

1. mechanics, 200 pages at most

2. lore, can be up to 1000 pages detailing how everything works in the setting

2 books, is plenty; in my opinion.
Book #1. Player Stuff
Book #2. DM / GM Stuff

fair! that's also good.

Quote from: Bruwulf on January 16, 2023, 06:31:12 PM
A lot of people don't like massive 600+ page tomes. Hell, I don't, and I own several. Much above about the 250-300-ish page "sweet spot" my liking of a book starts to decline.

Good point. Pathfinder 1e combines the player & gm books into one painfully large lump. I never liked it.

My decision to put my system into two books came down to a confluence of factors.

The first factor is that the total document is approximately 240k words.

The second factor is the bar none cheapest format for publishing is 6x9" (the most used format in the world).

This means that, at a reasonable font size, my material comes to around 720 pages and 6x9 books start getting difficult to keep open at about 400 pages... so I opted for two 360 page books.

From there I opted to put everything a player would need to access into a "Player's Guide"... character building, equipment (including magic items... once you've identified them a player is more likely than the GM to need to look up the rules for using them) and the general rules for combat, skill use, movement, etc.

Basically, if it's something a PC is likely to interact with, it's in the Players Guide (ex. Vehicle, structure and trap/hazard construction rules are in the Player's Guide because, while GMs use them often, PCs can also buy and construct such things).

The GMs Guide is all the material PC's don't typically interact with. Two-thirds of the book is pregen monsters. The rest is new GM advice (apparently prescient given D&D may no longer be the gateway to ttrpgs it used to be), charts and tables for inspiration on creating a setting and adventures, and rules for the environment, for creating afflictions (curses, diseases, lasting injuries), for assigning values for NPCs (ranging from "what sort of modifer should a village blacksmith have for their Engineering check if a PC needs some equipment repaired?" to fully statted individuals) and creating custom monsters.

The idea I had is that, last I checked, I should be able to retail each for about $30 and a player only needs one while the GM only needs the two.

I don't plan on releasing splats of new options. My supplements will be adventure sites and region books that will include new items (traps/hazards, vehicles, afflictions, monsters) created using the core rules. The value is in the time saved by providing settings and options that a GM doesn't have to do themselves.