My first pair of el-cheapos came with two head torch type set ups. I just cut the straps off one and velcro it to my helmet.
Works a treat and I generally just leave it on all the time.
Lights mount the same way as to the bars, easy peasy.
Mine are the magicshine style knockoffs, 1600Lm I think, and have so far been faultless over the last 18mths or so. Battery life has been great, never run out on a ride. Generally we are out for 1.5-2hrs and I run them on high on the trail, only low on the roads.
I bought a cheap solarstorm recently, claimed 5000Lm, which puts out a lower light than the old ones I had. Throws a good spread though.
All three lights together have cost less than $110 combined. I'd call that a bargain.
Mate has some Ay-ups he bought a few years back, roughly $400ish I think he said. I've never used them but they do look quality and the build and packaging is great. Even got in touch with him when they upgraded the lens. That's service.
But I've still got three lights for his one pair at a quarter of the price.