Dragon slayer books are not hard to make. They are a regular slayer. Any scribe who pumps out spellbooks sees tons of dragon slayers. Dragon slayers are only wanted over other regular slayers because they are higher end monsters. Unlike lizardman, troll, etc.
Now, that book would be extremely great if it was a REPTILE slayer. But as a dragon slayer, its still a basic slayer spellbook. super slayer books start out maybe 400k or so. a 3 mod dragon slayer, maybe worth 50-100k max. Depending on properties.
LMC is pretty easy to max out on a mage. On the other hand, if that book had SDI and/or mana regen, worth more than your current book.
A nice mana regen, dragon slayer, with SDI.. thats the perfect book your trying t get as a dragon slayer. LMC is easily reached by other items.