from their site :
Surface shipping and handling is 20% of the total order amount or a minimum of $15.00.
Air delivery is 40% of the total order amount or a minimum of $35.00.
I put an order in every couple of years for hunting gear etc. Have always gone with the Airmail, but have been talking to some people recently who have received the surface mail with a couple of weeks. Just depends on your luck.
I've never managed to avoid the Customs charges (x% of retail price inc. shipping), plus the carrier will stick a handling fee on top of that. You really have to do your homework, or you can end up paying a lot more than you thought.
having said that, the odd order is a lot cheaper than what I'd spend if I visited one of their stores!