This is not high enough volume to give a volume discount. If they want to order 1000 or so, THEN I'd consider a volume discount.
This is one of those "If everyone else was jumping off of the bridge, would you, too?" Just because you "heard" other places do volume discounts, doesn't mean you automatically do them. There's a whole science, math and business savvy logic involved in discounting.
WARNING! WARNING! BLATENT ADVERTISEMENT COMING UP!!!
There is an article coming up in a soon to be released issue of Cake Central magazine in which I address this very issue, with some excellent quotes and input from some nationally known marketing experts who I am privilaged to know as friends. Stayed tuned for details. Film at eleven!