Stepping sideways from the car aspect for a minute, I found that once I re-discovered cycling for local transport, my shoes would wear at a vastly reduced[1] rate, as I was walking less far. This was briefly offset by saddles destroying trousers, until I worked out that cycling-specific clothing (particularly the more presentable things like Endura Cruisers and MTB baggies) was a fair bit more robust in that department.
And then it's almost impossible to untangle the true costs of my transport cycling from my hobby cycling. But I don't care, because most of what I spend on hobby cycling is returned in physical (and to a lesser extent mental) health benefits that are effectively priceless.
I find it easy to justify spending on things which give a tangible safety improvement. Decent brakes; better lights; appropriate tyres. A set of Marathon Winters isn't cheap, until you compare it to the cost of some new clothes and a couple of physiotherapy sessions, let alone time off work.
Lots of things to factor in...
[1] I have an unusual gait that wears shoes from the inside out, so sturdy soles don't really help.
