Roughly the equivalent of 32 packs of cigarettes. At 20 a day, that's less than 5 weeks worth. And your shoes will last you 500+ miles per pair. At, say, 40 miles per week, that's 25 weeks of running. A bargain.
Just in case you are wondering why I'm making this particular comparison, I gave up smoking 8 years ago today!!! I think I'll treat myself to a new pair of shoes in celebration.