Most reputable online sellers should only be charging the cost of Priority shipping.
If it seems out of whack, find another seller. (I also won't buy from a site with inflated shipping.)
Check the flat rate prices here for your country - weight is maxed at 20lbs for Priority packages:
http://postcalc.usps.com/
I sometimes act as an "aggregater" for my overseas friends.
This way they can order from numerous sites, take advantage of free shipping and sales promotions, and have the package sent to my US address.
Also, they can buy from shops that don't normally ship overseas - like Connecting Threads.
If a shop won't take their cc or Paypal (because of THEIR address), then they just tell me what to order for them.
When they're done, I just pack it up in one big package and send it off to them.
They pay me via PayPal.
It's seamless, and requires minimum effort on my part.
Heck, I want to be helpful but let's not go overboard. ;-)
Yeah, it's a big postage bill, but they're used to it, and the abundance and variety of fabrics available from the US sites is always going to be larger and less expensive than these same fabrics in their own countries (shipping/business import tax).
Also, most seem to escape paying any import tax.
I think mostly on the FR Envelopes.
But that's never guaranteed.