I'm also in the UK. International shipping does definitely influence my decision of ticking the 'match international' box on some exchanges I've done, both due to shipping costs and conversely being afraid that high shipping costs on the other end will put someone off and I'll be shafted. Touch wood so far that hasn't happened though for the exchanges where I have done international.

As someone else mentioned, the key is to focus on weight. Royal Mail is definitely cheapest compared to courier companies and I always just get standard instead of bothering with tracking but do keep proof of posting. It's about £13 for 1kg, then progresses to about £23 for 2kg, so if I know what I want to buy is going to be a bit heavier I'll just order direct from a domestic-to-my-giftee website (usually the US in my experience, so many retailers will allow foreign card payment). It's a bit less fun, definitely, but more practical in some cases. Sometimes I'll do a main gift order that way but also send something small from the UK. Weight does influence my gift choices though as I know sending something that weighs 5kg+ just isn't realistic in terms of cost. Most times so far I've been able to find the perfect somethings within reasonable weight and postage price just fine.