Shoes are one of those things you get what you pay for. I run for exercise so know you get what you pay for.
Nike, Reebok, Asics, Adidas, Brooks, Saucony, etc (except for Skechers - they are junk) all hire scientists to study how the body moves and they make shoes that work with your biomechanics. The junk you get at Wal-Mart, Target, Payless, etc is just that - junk. They are cheap because there is no R&D, low quality materials and less padding.
Your best bet is to go to a running store and get fitted and see what works for you. Yes, you can spend $50-100+ for sneakers but once you know what you need, you can shop last year's models at considerable discount.
I'm lucky in that I can run in just about any name brand sneaker - my cheapest pair is a $39 Nike Dart I got at BJ's. Worked well for me.
Don't be put off by prices - once you F-up your feet you are in for a lifetime of pain and will never be right again.