My players have found a number of spell books and scrolls during their adventures and the idea has been mooted to purchase a blank spellbook and copy useful spells from the disparate sources into the new, single spellbook to be used as a "group spellbook". I have the following questions:
1)How much would this cost and take per spell/spell leve? It doesn't seem to fall under the category of adding a spell to one's repertoire or replacing a spell, nor does it really seem to fall under scroll creation.
2)How much are spellbooks worth? Like, they defeat a wizard and take his spellbook, how much can they sell it for?
2a)How much are formulae worth?
3)Do spellbooks/formula count towards the overall vlaue of a wizard's library or purposes of researching spells/creating magic items?
One issue is that, per RAW, every wizard's connection to magic is unique and personal. Part of why it takes so long to add a spell to your repotiore based on one you find written down is translating it because that wizard uses the metric system, writes in a counter-clockwise cypher, and bases energy flows off of an astrological system that also has elementalism thrown in for some reason. You use the Imperial system, write vertically alternating direction every two lines, and believe that magic is derived from a combination of spirits, ley lines, and things people whisper at night.
I believe Susan's interpretation is correct, and I would likely make a similar ruling in any campaign of my own. Magic in ACKs is very specifically not technology. There's a lot of idiosyncracies that keep mages from collaborating with each other in large numbers, in addition to mistrust. I remember reading something from Alex about how in his campaigns, most mages won't even agree to exchange spells unless both are already capable of casting charm person on each other for mutually assured trust.
While that makes sense for campaigns that operate in that manner (which ours may or may not -- I'm in thirdkingdom's game, btw), there's still got to be an economic mechanism for the cost of blank spellbooks, sellable price of found spellbooks, and associated costs of the formulae used in the creation of magic items.
With regards to the "shared" spellbook, I'd imagine it's possible for one mage to be the primary scribe within the spellbook (it's essentially theirs) and for other mages to have permission to copy from it, if magic is not held so tightly by this group compared to other mages or groups in other campaigns.
For what it's worth, I'd price the spells in the spellbook the same as spells in a scroll, as a found spellbook is essentially just a sturdier scroll of spells. That pricing isn't clear, either, so I've eyeballed it based on the costs of hiring a cast spell from a caster (though that should be multipled by some factor, IMO, since a spell on a scroll can be added to one's spellbook/repertoire and cast a much greater number of times than a hired spell casting).
These threads talk about copying spells in general, which might help you in determining what you want to do with the backup/group spellbook idea in your campaign:
I've posted in our OOC thread, but what I'm doing is this:
*A spellbook has a value equal to the number of common spells contained within x500 gp/level.
*Rare spells (i.e. those not found within Core or PC) are worth 1500 gp/level.
*Spellbooks follow the same rule regarding magic items in terms of buying and selling.
*When building a library for magical research spellbooks are considered to be worth one tenth their total value. Therefore, a spell book containing three 1st level, two 2nd level and one 3rd level common spells would be worth a total of 500 gp and would count towards 500 gp of a magical research library.
I'm going to also go ahead and say that formula have a cost equal to what they save in crafting a magical item and are also governed by the same rules as magical items when it comes to buying and selling them.
We know it's possible to have a spell formula in your spellbook but not in your repertoire, since the rules state on p 67 that replacing a spell with another spell in your repertoire doesn't cause you to lose the replaced spell.
Alex has commented that, while it's not covered in the rules, he would say a caster can create a backup spellbook. But he says that the backup spellbook needs to be scribed anew once the caster levels, because the spells aren't being "actively maintained with metaphysical data".
However, if you replace a spell in your repertoire and it's still in your main spellbook, you're not actively maintaining that spell. Yet the rules don't require you to re-scribe that one all over again every time you level.
If you find a spell that's too high level for you to cast, the rules say you can save it and put it in your repertoire in the future, when you level up. But when you level up, wouldn't that spell be useless to you because you weren't actively maintaining it with metaphysical data, as per Alex's house rule? Why is it that formula in other mages' found spellbooks keep forever but formula in your backup spellbook go "stale" after you level once?
It also says in the rulebook on p 67 that a spellbook can be read by any arcane spellcaster who can read the language the spellbook is written in. That contradicts all the comments here about how every caster's formula is a unique snowflake that no one else can comprehend. My interpretation is that the formula are all the same, it's the way you incorporate that formula into your repertoire that's unique. Otherwise, mages would never be able to gain spells from scrolls or spellbooks; they'd have to create their own personal version of every spell they cast.
The rules state that "powerful arcane spellcasters generally build large libraries of spell formula and scrolls so that they can replace the spells in their repertoire with new spells when the situation calls for it". Do we really think they're re-copying all those spells every time they level?