Do you want to 'be seen' or to see where you are going? Whichever of these outcomes you are seeking, you also need to outline the likely circumstances of use. Daytime use? At night? Both? City traffic? Trail, bike path or unlit areas? Do you have a front light or a rear in mind - or both?
All of these factors have a direct bearing on your choice and on what you need to consider - and on what you are asking others to consider in offering advice. Up to the $40 price you have nominated - if you are looking at a modest, 'pocketable' or easily removed lighting set for commuting that is likely to be reliable and flexible for everyday use them you can't go by lights made by Cateye. Or quite a few high quality 'brand name' lights in the same vein such as those made by Cygolite, Smart, PlanetBike, Lezyne etc etc. And then there are (literally) 100s of lesser known or 'Chinese' lights which can be had very cheaply. I've found that - in this latter category - lights made by Tioga, Azur and Electron (all to a very similar pattern) offer very good value.
It's important to note that many of these lights will operate to similar levels of 'brightness' with the best buying-choice criteria likely to be based on mechanical or switch construction or design. It's worth reading reviews at Amazon, Wiggle etc as any problems tend to be documented there pretty smartly!
Savvas.