Send your package from an US Post Office, it's less expensive than UPS and FedEx. At the post office the agent will give you all the prices /options for your package. They also have packing supplies if you need a box and tape.
Thank you for your reply!
We sent quite a few boxes back home to Australia and did so through the US postal service. It's not cheap but it's way better than lugging around everything in your case!
We would grab a box from the post office, take it back to our hotel, fill it then take it back to the PO to send. We found that parcels took less than a week to arrive back home and had no problems with anything being damaged.
Everything goes by airmail these days; there is no cheap boat rate. I have young relatives in New Zealand to whom I sometimes send gifts for birthdays and Christmas and the postage is often more than the value of the gifts. I have had pretty good luck with the US Postal Service. The only other way I have sent things is by Fed Ex and I had some problems there.
The USPS has a couple of different arrangements. They have a couple of standard size boxes you can get at the post office, each of which goes for a fixed flat rate regardless of what is in it. I was using this once when an agent pointed out to me that it would have been quite a bit cheaper if I had just put the stuff in any old box (subject to size limitations spelled out on USPS site) and paid by weight, which is what I do now. I believe you can also use things like tyvek and padded envelopes, if they work for what you are shipping, which should cut down on yor cost assuming the envelopes weigh less than boxes.
Most of this info is on the USPS website, which I often check before I go in with this type of stuff, but I frankly find the info I most want is frequently hard to find and requires a lot of patience to get.