Spellbooks are so rare because they can't be copied, not without extensive study by a powerful Mage, or a class with similar Skills. Not even a high leveled mage could simply do it, as it requires a specialized class such as [Magical Scribe]. More importantly, scribing a spell is only possible for someone of an equal of higher level than the spell itself. For instance, for a Tier 4 spell, one would need to be around Level 40 or higher.
Most spellbooks found today are of a lower quality than those found hundreds of years ago aligning with the degradation of magical knowledge as a whole that is seen throughout the story. One surviving spellbook from three hundred years ago is a first edition tome of Rihal currently in the possession of Krshia Silverfang. This spellbook contains multiple lower tier spells and is significantly easier to learn from than most modern spellbooks.
- Just one book costs several hundred gold coins, sometimes even a thousand, and that's for low-Tier spells.