I own these, and wear pretty much only these - the rest of my cotton uniqlo/whatever socks I save for exercising
80% lambswool 15% nylon 5% spandex, incredibly comfortable, hold up well to washing, and come to about $4 AUD shipped via ebay
Just stock up on black, light grey and dark grey - be warned though, you can only purchase 2 pairs of each colour and no more than 7 pairs total in every order, and you can only buy no more than 7 pairs every 10 days - I now have 4 pairs in each of the three colours, which is enough for me