I think it might be a mistake to think that your target demographic would be LetsRunners... poorish people that are recently out of school and already have a running routine that they've established over many years probably are going to be slow to purchase an application like this. If you head over to the RunnersWorld board (really any running board that has a glossy, advertisement-filled magazine associated with it) people will probably lose their mind and start a bidding war to buy equity in your "new company". I bet you'd absolutely be able to charge money for it, you just have to recognize the demographic who'd be paying for it.