I've often bought stuff from the United States & Europe & thought that the specified postage cost was either not mentioned or i thought that the cost was way over what i thought it should be. Sometimes sellers from overseas just use some feeble ebay mechanism to work it out, guess a cost or they just cant be bothered to put on a price for posting overseas.
I look up the local postal service say for the US that is the US postal Service. I then go to the postage calculator that is very easy to use & look up the size & approximate weight of what is been sent dont forget to account for packaging I then email the seller to let them know I'm interested & could they send the item via your preferred method as per the postal service website. Obviously sellers will often add on a certain amount for packaging & handling so dont expect them to use the actual postage cost. However at least you know that whatever price they confirm for that service you will know what the handling fee is. Some services include insurance in the postage cost(like Royal mail) but most do not.
Be aware that the import value of goods into the UK from outside of the EU were duty will be applied for is only £36 for a gift & £18 for commercial products. This has remained the same for many years now & is totally out of line with other Westernized countries! Importing for US buyers without attracting import duty is $100. If a US citizen buys goods over here they can send up to $200 worth of goods to themselves in any amount of packages without any hassle from the US custms.
Most US sellers will not send other than via a trackable service, though priority mail flat rate envelope should be secure enough for most sellers. On the United States postal Service website you can find out the cost of extra insurance so can ensure that you are not been ripped off.
United States Postal Service(USPS) cheapest postage for smaller items to UK is via 1st class international, a lot of sellers wont quote this but just ask. Flat rate envelope & the flat rate small box are a fixed price for up to 4lb in weight and can offer excellent value for money in terms of actual postage cost. Canada post is also very easy to navigate, their are some very cheap services from Canada to the Uk, ask the seller, sometimes they are not aware of them
Swiss Post, cheapest is Economy Maxi Letter 8Swiss Francs for 500g up to 90cm combined H W L, max 60cm length 12CHF for up to 1kg (2009 prices)
French post, La Poste has an English version for those who have just moved to the country. Click on the Already living in France on the web page & then the section sending parcels & how much it costs.
German post. Deutsche Post website is pretty easy to navigate even if you do not understand any German. German post is far and away the cheapest of the other European postal services.