A few years ago I compared the cost of walking, cycling, train and car. I've long since lost the piece of paper now, but there was surprisingly little difference. It depends greatly on what assumptions you make of course, particularly with the fixed costs like road tax and insurance, and the train cost depends whether you count mileage the way the train goes, the way the road goes, or the way the crow flies. Walking and cycling work out pretty expensive if you include the cost of accommodation and time.
I'm curious how this was looked at, and coincidentally had the same discussion whilst walking last weekend as to the overall costs of walking versus cycling and other hobbies such as the gym, and outdoor running as an alternative to that.
There are certainly a few ways of looking at this 1) functional locomotion for work 2) functional locomotion for recreational use (riding to the cinema, for example), and 3) recreational locomotion. I very much doubt that the maintenance cost of cycling is much greater than £150-200 per year for daily use, which would cover a service, oils, and at a push, tyres. The same with hiking, the expense will be damaged equipment, required washing materials/electricity use to do so, versus a direct method of moving.
To the question of boot wear, the factors would seem to be gait (distribution of weight across the boot and walking motion), and the weight of the individual, coupled with what materials they are walking on. The physical material 'limit' of the method used to bind the boot together will be matched or exceeded more frequently when a walker has an atypical gait or weight, and will likely lead to increased wear.
Bear in mind that this will likely be compound degradation, though, and extremely hard to model due to the interaction of the boot with the movement of the foot, and the difficulty in modelling a standard walking surface (since jumping, pushing, kicking, walking and even running motions will all have different impact on those material limits). There is also the problem of one component of the boot failing and causing a cascade of other failures do to the increase in stress on other components, a case in point being stitches which tend to fail in groups.
If I was modelling it, I'd just record how far I walked in a walking log, and make a point to make a rough note of conditions - and crucially, maintain your boots well. Clean them after use, frequently wax them, and make sure you don't "kick off" mud or use them as a form of blunt force instrument - all factors which are likely to have a much greater effect on the integrity of the boots than pure miles walked. It is worth considering, if you walk for one day a week, every week a year, then you are likely a very keen walker - yet you will only be wearing your boots directly for 3.5% of the year. It is why I'd considering putting some thought to regular cleaning/storage/ventilation and damp if you have a quality pair of boots and want them to last.
