I'd offer to buy it from USA and send you the steam code, but there's no guarantee that valve won't revoke and remove the game after a few weeks since its different territory (I assume you live in UK since you've mentioned GBP). They did that with orange box purchases when people bought legit asian steam serials, then put them into USA steam accounts. Then they told everyone who had purchased them, tough crap go buy it again.
Actually, I had no problems when I sent money over to another member of Bluesnews and got them to gift the game to me - that was for a game (Far Cry 2) that wasn't available at the time here in the UK. But I wouldn't recommend it just for saving a bit of money; I'd only risk it if the title isn't available. Just accept you're going to pay a bit more or hold off for the inevitable sale.