Considering you can buy them for 15 GP each from any non-faction mage shop, and 10 GP when they are low faction priced, and you can't put them on commodity deeds, adding a "convenience" surcharge of 2 - 3 GP per item over NPC price, is the usual practice from what I recall, same as with reagents. (if you have someone, such as a stinky orc, wanting to churn out spell books or someone doing the heartwood quests, you can probably add 5 or more to the price, maybe more, if you have a lot because it takes a good bit of time to farm the vendors and haul the scrolls.)
-Skylark