Dave -
My experience is US suppliers, almost without exception, charge way too much for international shipping. After getting several quotations from US tire suppliers, I got tired of the insane shipping quotes I kept getting. Coker was kind enough to give me a $1,270 shipping quote for 4 tires. Thanks but no thanks. From Australia the same order was quoted with $195 in shipping, but I have to wait 10 days. I'll wait the 10 days, thanks.
By the time you work through shipping, it'll be cheaper for me to order from either Australia or the UK because shipping will probably be less than half the cost, so it doesn't matter what the price of the tire is, it will be cheaper if I get it from somewhere where they know what an export economy is.
The only guy in the US I've ever had a reasonable response on shipping costs was Norman Nock over at BCS, but then again he's English!