18650 based flashlights in a handlebar clamp do surprisingly well also for little money - I bought this for $20 to use as a backup:
http://www.ebay.com/itm/271032780742
Add a handlebar clamp and you're good to go, this one works well for me:
http://www.ebay.com/itm/380604482446

In the low-budget "designed to be a bike light" realm, I've got one of the "1800 lumen" bike lights currently being sold on ebay for around $30. I add a $6 lens to spread the beam a bit. I think it's pretty good. The advantage over a flashlight is that the battery lasts a lot longer (2.5 hours instead of 1, if you run on high). Some work is needed to make the battery waterproof; a plastic bag will probably be good enough, though I 3D printed a case for mine.

It really lights things up pretty well. What you lose for the low price is durability. I'm very careful with my equipment and I expect it to last a year or two before I have to start playing with it (replacing broken connectors, etc).

If you want to get a light that's bright, waterproof, durable and everything, try the Cygolite Expellion 700, which is an awesome light and available < $120.