For a $50 budget your only options are the cheap Chinese lights and extra batteries. Some of these lights are very good, others not so great. I use a single LED light that is bright enough for my city riding, but I've never taken it on a dark country road. It is rated higher than what was available just a few years ago though so it should be plenty bright for that too. http://www.keygos.com/product_info.php?products_id=1156 is the one I have.

If you check around that website you'll see others too, but I can't say that I've tried them. The one I mention comes with everything, including the batteries and charger, others don't. I also wear it on my head and use it as my grilling light, basement light, and any other time I need a flashlight. Put it on strobe and aim it at your disco ball and you have an instant dance party. (This isn't my idea, some really cute girl stopped me and suggested it one night when I was riding through hipster Brooklyn.)