For a couple months now I've been toying with the idea of starting a (hopefully) long-term thread in BF/Commuting about cost per mile of bikes (although it could go in general as well).

A working-condition road find is 0/mi from the instant you first set in motion, until you first have to replace a tube or a brake pad or something.

A bike that you pay $10000 (or even $1) for, but it only sits in the garage and is never ridden, has infinite $/mi.

Everything else is in between. Discuss.

The $/mi metric can be applied to individual bikes, or whole stables. It gets tricky (see ship-of-Theseus problem) for somebody that swaps parts between bikes a lot.

If you sell a bike you can deduct the proceeds from the total bike cost and 'close out' that account. (If you flip the bike for more than you put into it, your $/mi is negative!)

But if you start to factor benefit into the equation (I paid X for the bike, but saved Y because of riding instead of driving, or saving bus fare, or whatever), it gets too complicated I think. I'm not so interested in comparing bike cost to car cost, as much as all of us comparing our bike costs to each others'