Aldi do a pack of three torches. Three torches, 9LEDs each, plus batteries (3xAAA each) for £4.99. Works out at £1.66ish a torch.
They work well as front lights about town. Not focussed enough perhaps for seeing the road on an unlit road, but nice and bright for being seen by. Easily fixed to handlebars with zipties, or oversized O rings or similar. If only there was a matching rear light.
Well, you need a torch and some of this:
This happens to be off an old Landrover. You need enough for a disc 2.5cm in diameter, so a nice flat bit picked up off the road might do.
You hacksaw it down to a square a little bit bigger than you want to end up with, and then you need one of these:
By which I mean a belt sander, not MFWHTBAB, although having a MFWHTBAB is very handy in many situations. Or just some sand paper. (In place of the sander, not MFWHTBAB)
Sand down to a disc of the right size to fit just inside the bevel around the lens of the torch. Apply some araldite to the rim:
and press in the red lens.
Presto! At less than £2, they are cheap enough to leave zip tied to the bike! MFWHTBAB has one rear and two front ziptied to Granville the Hungarian folder (thus increasing the value of the bike by 33%!)