The cost of the actual book is minor (15 gp as I recall).
The real cost is in the scribing.
I don't think it is fair to charge them the cost of used up scrolls out of starting equipment. If you are doing that, better charge other characters for any potions they may have drunk in the past or other single use items they may have used up.
Charging for scribing costs to put it in the book quickly makes it worthwhile to have a Boccom's Blessed Book. Just make sure you buy one of these for extra spells, then ask the GM how many spells you came across which you could scribe.
The real cost is in the scribing.
I don't think it is fair to charge them the cost of used up scrolls out of starting equipment. If you are doing that, better charge other characters for any potions they may have drunk in the past or other single use items they may have used up.
Charging for scribing costs to put it in the book quickly makes it worthwhile to have a Boccom's Blessed Book. Just make sure you buy one of these for extra spells, then ask the GM how many spells you came across which you could scribe.