It is a lottery and one that the odds are not on your side.
I used to buy a lot of DVDs from American before the .co.uk site and Play took off, the Post Office didn't catch items as often then (Amazon always label items correctly with prices on the sticker).
If you send it via courier then it is almost certain you will get stung for it. The last 2 items I bought from the states I could not source from the UK at the time so had to buy from the US, so there was no comparable price, each got stung good and proper. It was a nightmare trying to find £50 in cash I tell you, I had to raid my piggybank and give the UPS guy £20 in change as I only had £30 in notes in my wallet.