You can buy them new for £20 delivered and they come with cleats. Cleats on their own cost £10 to £15 and they wear out so its always usefull to have some spare. That, in my opinion, makes second hand M520s without cleats worth next to nothing.
Good ones do sell on ebay for around £10 plus postage without cleats though, but not to me!!!
Tidy M540s are worth a look on ebay though as they sell for much the same as 520s but cost £35 new. I picked up a beaten to sh*t pair of 540s once for 99p plus a few quid postage and when they turned up the bearings were perfect. They are still going stong on my commuter thousands of miles later