I think UCD used to buy them in for E50 a pop - and that's a few years ago now, so add another 5/10 quid today maybe? It's mad how expensive they are.
Then the ones you don't sell are kickers. If you buy, say, 50 @ E50 and sell 40 @ E60, then you're down a hundred quid even though you've sold 80% of what you bought