Is there any mention in the listing that the seller offers a combined shipping rate? Some do, some don't. You can use the Ask a question link on the right side of the listing page to contact the seller, if there is no information relating to this in the listing. Tell him what you would like to buy, and ask what the combined rate for those items would be.
Is your seller in the US? If so, ask what it would cost to have all these items delivered USPS First Class International. (It's much cheaper than Priority, and you are cutting costs, you say).
Some listings clearly state that the seller offers a combined rate, what it costs for each additional item, and when you buy you pay the lowered amount at the check-out. These sellers consider redundant questions about combined shipping to be an infuriating nag. So read the listing, top to bottom.
