Free!
I have tried many different lights on the bike. If you just want to be seen most cheap type ones from the local bike shop will do (1 flashing, 1 static) but if you want to see on unlit county lanes at night you need 'proper' lighting which usually costs. I used to have a twin beam Cateye with bottle cage battery which was great but heavy and not too cheap. Not expecting miracles from this deal but X2 bar mounted might be a good compromise.