There are lights specifically made for bikes, but there are also much cheaper general purpose lights. I use a flashlight like this, and affix it securely to my handlebars with interlocked hose clamps. I find that the zoomable head is able to adjust the beam width so I get coverage I like without wasting light up in the air (bouncing off of street signs) or in drivers' eyes. If you go with a light like that you want to find a kit that comes with a charger and a battery, and then also shop for one or two high-quality 18650 batteries (they're like AAs on steroids) for like $7-10 each, and you should be set for under $30.

Another lower-cost option is a "magicshine clone", like this. The head is very light and goes on the handlebars, and has a power cable going out to the bigger battery case which you attach to your frame somewhere (some people cut the top off a waterbottle and keep it in the bottle cage, maybe along with a patch kit etc). These are bright enough, but have a VERY narrow beam, making a bright circular spot about a foot in diameter ~10ft in front of you. If you get this you will want to get a spreader lens. That spreads it out either in the wide or long direction (depending how you rotate it in there), according to your preference.

If you're riding at night you will also want a bright red blinking tail light. It's easier to get something decent for not much $ here, since you only need light to be seen, not light to see by. I've used PlanetBike Blinky, it's pretty good. But I think the favorite light out there is any model Cygolite Hotshot. Very much worth the $30-ish they cost.