I'm big on Goodwill, Thrift stores, etc. and amazing what you can find in them! I recently picked up 2 pairs of new shoes at a local Goodwill store. They weren't dirt cheap but a better price than in the shoe store or even WalMart.
Lisa, has a great idea, Sport Mart, Sports Authority but they will be pricier.
I think a cheap pair of Keds would do and probably get more use later, too!