I ship worldwide and pay the 5p for US/Canada listing. Postage-wise, I give a flat UK price and a flat international rate - I weigh the item then look up the price to post to Europe on Royal Mail's website as international costs seem to be hugely complicated and I've been out of pocket before by underestimating. I then put in my listing, in bold text, that the international rate given only covers Europe and postage to US/Canada/Australia etc will be more.
Generally this works okay, but I've had three auctions finish last weekend where Canadian/Australian buyers have just paid the international rate and I've then had to message them to ask for more to cover air mail (but offer to post surface mail for the rate they've paid) which I don't like doing as (1) I am British so hate mentioning money at all 
and (2) I'm always worried they're going to kick off, though so far everyone has been fine with it.
The only other alternatives seem to be either putting a higher rate and ripping off European buyers or listing all the different rates separately, which would take forever and wouldn't be worth it as I don't sell that much stuff to longhaul buyers - though enough to make me not want to stop shipping worldwide.
Is there an easier way of doing this that I've missed?