I currently have a $20 light from walmart. I'm not a fan of it because the first one fell off the bike while I was riding. Had to buy another one
Another time, I bought a bike light that also came with a rear light. this was on ebay and it only cost $3. However, it was obviously made of cheap materials because on a 23 degree day, the plastic snapped when I tried to take it off.
It would be nice to have reliable front and rear bike lights without having to spend $50+. That said, what bike light do you use?