I opened a Click-n-ship acct with U.S. Post Office, and I ship from my studio.
My parcels are certainly smaller than yours. Go to USPS.com and print out their rate charts. Priority Flat Rate is cheapest, and they have large boxes. for International, you can ship first class, but there are size restrictions and you can't get insurance for 1st Class parcel. Priority International flat Rate can be insured.
I ship to Canada, the EU, and Israel, Australia, and New Zealand.
Download customer service manual in pdf.
Good luck!
lee boojamra