Sounds like a good idea... with a little modification such as maybe make it giant so it doesnt fit into bags, and is on par with the price of however many daggers it has on it.
Lets say in a roleplay sense the merchant has found an efficient way to put a multitude of daggers together. Simple cardboard box like a wedge which has 400 or whatever daggers stacked in this box. (Getting too in depth on the description) but anyways he packs em in there and sells them at bulk price.
Saves the pain of clicking buy 20 times and also doesnt have the benefit of doubling as a bag when daggers are low as a drawback.
Id say the most commonly bought items from a merchant are bandages, food, water, and throwing items. a bulk solution could be applied to all of them in a balanced way
Box of Throwing Daggers
GIANT ITEM
Weight: 3.0
CHARGES: 20
Effect: Summon Throwing Daggers
All/All