As a "non-runner" who just needs running shoes for the gym and walking around, I found great luck at Thrift Stores. What I found us a marathoner will buy a pair of Nike's and run that 600-700km until they are "spent" and give them to Goodwill. While they aren't good for running anymore, I found most to have plenty of sole left for 6-7 months of walking and going to the gym, all for around $10.

This is probably not the best for my feet, but when I bust a hole where my big toe goes I feel less bad because I spent $10 and not $100.