$20 on a light? $100 on a bike from Walmart? I understand that you have to start somewhere. But, if you valued the opinions of most people on these forums, you would not have started by buying a bicycle from Walmart. I guess it's fine if you are just an occassional rider (1-2 time per month.)

For $20 for a light I don't think you will find much that will help you "see" the road better at night (at least not at a speed that exceeds 10 mph.) You may be able to find a flashlight (hopefully with a flash mode) that will help you be seen better. Check out dealextreme.com for some fairly inexpensive (many under $20) lights:

http://dealextreme.com/products.dx/category.942

get the ones that are rated with the highest number of "lumens." 200 lumens is fairly bright.

this link is for a universal bike mount that cost $1.54

http://dealextreme.com/details.dx/sku.8274

shipping is free on your order.

That is about the most inexpensive suggestion that I can give to you. For me... the most important piece of equipment on my bike for riding at night are my lights. If I am not absolutely positive that drivers can see me, then I don't ride. I have a 900 lumen light on my handlebar, 2 900 lumen lights on my fork, and a 200 lumen light on my helmet. I also have 2 planet bike superflash tail lights, and a cateye 1000 tail light with 10 led's on the rear. If you are riding on the road, it's really important that cars can see you from behind (that's assuming that you are riding on the right side of the road.)

I've spent about $450 for the lighting on my bicycle. That's how important it is to me. For the front lights about $325 for 2900 lumens would be considered a "value" to many cyclists (I purchases most of my lights from dealextreme.com.)

Whatever you decide, be safe riding in the dark.