don't take the ebuyer price as a guide. They'll have bought that a couple of years ago and it'll be sitting around in stock unsold because most people don't buy the top end CPU of a particular family. Store prices will always be based on the wholesale price a component was purchased at (plus profit margin, obviously), rather than a realistic selling price in the current market. Legacy components also tend to attract significant mark-up at retail due to generally low supply. Look at the cost of SDR and DDR1 memory, after all...
BUT, having said that...
Socket 775 quads, and particularly the Q6600 / QX6700, are holding their
second hand sale value very well, mainly because the subsequent components haven't been a huge advance - particularly on s775 for people looking to upgrade from a dual core. The Q8x00 and Q9x00 have less L2 cache are not particularly quicker (the Q9x50 is a different matter, but see my earlier comment about top end processors
), and the older quads are compatible with more motherboards, so they're a very desirable upgrade option for s775 - leading to high demand.
At the same time, they were such good performers that without going to i7 - and particularly i7 9x0 - there's not a great deal of performance gain to be got out of doing a full system upgrade at the minute - spending hundreds on an i5 750 plus new mobo and RAM isn't going to get you much real world improvement. As a result, there are very few people replacing Q6600/QX6700, so there is a low supply to the market.
High demand + low supply will inevitably lead to high prices.