Let's see... 32,380 km... Call it about $1700 for the bike... Plus... uhm... at least a dozen chains, a few cassettes, lots of tires... a couple wheels... I think I'm probably at a bit over 10 cents per km.
@Criggie, for a home made head rest, try to avoid metal, wood or hard plastic that can damage your head if the softer parts fail for whatever reason. The one I have, on the one bike came installed, has a triangle frame, where the two legs of the triangle fit into the uprights of its seat, the metal of the headrest going up above the danger point for me.
I have not often used it, the seat angle is such that I can easily keep my head upright and leaning back against the head rest does influence the balance and thereby the steering of the bike.
I can see the advantages when the seat back is farther down.
Sounds like the gearing I ended up with, when the new gears were installed. Last time I tested out the higher (faster) gear, I was going down hill as fast as I dared to go when I stopped peddling and gearing up and had half of the gears left.