As they cost about .15 BTC each to make (yes, I know this is a guess but it is an educated one), a selling price of .5 BTC each would be fair and also allow they buyer to actually make a profit.  At almost 1 BTC I do not see a profit in them with difficulty growing.  On top of that, buying from them you know that this just allows them to put up more of their own hashing power (since they pay so much less for it) without going over 50%.  You are doing them a favor at this point.