DX M650 cantis are every bit as good as the XT M734's and you should be able to pick up a full set with all the hardware for about £20...XTR M900 your looking at more like £45 at least!
There aint. Lot to choose. A bit of rigid alloy that holds a brake pad/block. Provided there setup properly thaere's not much to choose between nine out of ten of them.