My semi-DIY bike light
Out of curiosity I bought a ~13.50 € cheap Chinese 3-mode flashlight with CREE XR-E Q3 LED (claimed 120 lm). I found it quite bright, but runtime of ~1.2 hours on 3 AAA 1000 mAh NiMH cells is not good. So I got another cheap light for ~7.50 € from local supermarket, which turned out to be direct-drive (no constant current circuitry or different modes) CREE XP-E with a little higher luminous efficacy.
So I dismantled everything and built a 3-mode XP-E light of about 150 lm (calculated) output and used one tailcap, ballpoint pen, copper braiding, microphone cable, IEC power connector, two switches (on-off tumbler and on-(off) push-button for easy mode changing), low-voltage power connectors, battery holders for 3xAA batteries, cheap digicam case and various other small bits'n'pieces to hack together an external battery pack of 4...5 Ah (I've not bought the NiMH cells yet). Also made a crude shallow parabolic reflector from a piece of aluminum sheet to better harness the LED output. Around 28 € total ex. cells, which will be another ~25 € (for a comparison, non-rechargeable Cateye Econom Force HL-540 is around 60 € without batteries (4xAA cells), is claimed 170 lm and 2 hours runtime on high setting) .
Future upgrades might be CREE XM-L2 LED and different driver for ~900 lm output at high and ~400 lm at medium settings - but heatsinking might become a problem, even XP-E at around 600 mA warms the flashlight body up pretty well, XM-L2 at 3 A would need a whole new body. Maybe Li-Ion cells for battery, plus a suitable charger (the latter are notoriously hard to find and cost an arm and leg where I live, that's why I opted for NiMH for now).