People can't even agree what `usable lighting' is. For example, I find that this 1w 50 lumen light makes plenty of light to see with, and lasts about 4 hours at maximum brightness. I wouldn't go offroading with it, but for road riding it's adequate -- it lights your path. If not enough light, I guess I could get seven more of them and rechargeable batteries and a few chargers for all of them for under $100, mount them all to my bike.

Though perhaps they don't qualify as a bike manufacturer? If not, the Planet Bike Blaze 1w is similar -- similar brightness, lasts longer, uses more convenient 2xAA rather than 4xAAA batteries, but costs considerably more. Still, you could get two for under $100.

I'm quite happy with my P7 lights and they're a great deal, granted, but as far as I know they don't go cheaper than $30 or so, and you need to spend $10 more for two batteries and $5-$12 more for a charger and $1.50 more for a mount. It's not quite $20.

I also have a Cygolite 135 lumen light that was $75 or so after sale and discounts, and it's very adequate. It lasts about 4 hours with the included NiMH battery. It puts out less light than the P7 flashlight, but the beam pattern is far superior. It's not a better bargain, but it's also bike specific and under $100 and puts out a lot of light exactly where you need it.