Dependent on the shoe, you can probably eke around 5-600 miles out of a pair of road shoes. It can vary though, I usually get 6 months out of a road pair but my last lot only lasted around 4, definitely a good bit under what I was expecting.
Off-road shoes are a different beast, as long as you have enough tread then I know people who hvae literally run in them until they've fallen off their feet!