Ian
I bought a pair of Tesco L.E.D. "super torches " from Tesco ,they cost me £7 each last autumn ( thats with batteries ). I live between Aberdeen and Inverness ,and only have time to ride in the evenings on unlit (unpopulated ) roads,and I can see fine with them.
They were recomended by the local mountain bike club,i'v used mine off road on forest tracks at night,but they arn't good enough for fast single track.
I made mountings out of 25mm thick high density foam,and cable ties, If you don't fancy making the mounts ,I could make you a set.
Lee