Andrew at the Bottle Shop once explained his prices to me - some of the more esoteric stuff isn't available through the usual distributors, so he has to import it himself. Add the cost of doing so to the hefty import duty (even within the EU) and his prices for things like De Molen seem more reasonable (we can't all live round the corner from the brewery... Spit!).
I'm reminded of the time I paid nearly a tenner for a shot of vintage rum in a Cuban bar in Islington. The tosser barman pointed out that the same rum costs less for the whole bottle in Cuba. Yes, I replied, but how much does a flight to Cuba cost? It was bloody good rum, I might add - worth the price for an occasional special treat.
Even so, that £14.25 bottle at Sourced is outrageous. And I agree with the general tenor of the article that some of these "special edition" beers are way overpriced - and not all that good either. (I'm looking at you, Brewdog.)