You can bag a set of these on the web for less than 80 quid, I was lucky and got mine as part of a bike deal and paid only £50

I currently run XTR spd's and wont go anywhere else. I've tried the cheaper 520's and the bearings went and the "precise" feel wasn't there, don't know how or why, but it wasn't. I've also tried some expensive ritcheys and the bearings went on them aswell. With the XTR's they just work and work very well. Now for the price they are then they should, but they do go through a lot of crap and do not get the servicing attention other parts of the bike gets. I strip and clen and greese mine about once a year and that seems to be enough.