If you're keeping the motherboard that the E4600 is in then you could try something like this: http://www.amazon.com/gp/offer-listing/B000LRMR26/ref=dp_olp_used?ie=UTF8&condition=used
for $45. It's socket 775 like your E4600 but I would need to know the specs of your board to see what FSB speeds it supports... I know that the E4600 is only 800mhz where as the Q6600 is 1066mhz. Can you tell me what motherboard you're using?