Careful with guessing the quantity you are quoting. If you guess you should quote on 500 and he only wants 50 he will want the same price. Get an estimate of quantity from him then make sure your quote allows for more and less than that quantity.
I quoted a job recently that the customer asked about pricing for 100 items, turns out they could only "afford" to buy 10 but they wanted to see the 100 pricing. I'm glad I did a written quote for 1-10 as well as 100+.

Gary