Shipping charges on small orders can be tough. Unless something can fit in a flat envelope, I haven't figured out how to ship anything for much less that $5.00. Picking, packing, and boxing an order takes more time than anyone could possibly make on a small order. If they are adding an extra $1.00 or so to cover time, boxes, bubble wrap, tape, etc, etc, they still aren't making money on the shipping. If they do it for less than that they are losing money on your order. Which is nice from a customer's standpoint, but not a good way to stay in business in the long run.
I usually try to plan ahead to get my supplies at a shoot or to combine them into bigger orders so that I can minimize shipping charges.