I’ve been retired since 2012. I bicycle commuted year round the last 10 years in Iowa on a 7 speed (Sachs IGH) city bike I bought at a German Dept. store for 268DM (approx. $135). I replaced the saddle with a Brooks B-66 which I had already, but would have cost about $100 to buy new (and well worth it.), I previously modified the bike while in Germany with different handlebars and seat post which probably cost around 40DM ($20) total. Bell and mirror cost $30. I bought no bicycle specific clothes. I commuted an estimated 50,000 miles on that bike during that time. I spent almost zero time doing any maintenance or clean up of the bicycle other than replacing the chain about once a year/5000 miles and periodic tightening/replacing spokes on the rear wheel. Rode it to and from work no matter how cold, or bad the salt was on the winter roads.

Estimated bicycle related expenses over those 10 years; all costs are approximations:
$200 on different lighting setups with perhaps an additional $50 on rechargeable batteries.
$100 on bicycle basket and rack replacements.
$90 for chain replacement every 5000 miles.
$20 on spokes.
$40 for bottom bracket overhaul at the LBS.
$100 for an IGH maintenance by Yellow Jersey Bicycle Store after about 35,000 miles.
$500 for 13 tires; replaced front tire about every 15,000 miles, rear tire every 5,000. Schwalbe Marathons (not Marathon Plus) 622-47mm cost about $30-$40 each.
$100 for bicycle specific tools such as patch kits, chain breaker etc. All other tools such as wrenches, screw drivers, vise, I bought previously and are available regardless of bicycle ownership/use.

I am sure I spent money on other stuff and doo-dads but the costs were too insignificant to remember or consider.

I don’t consider food as only fuel or an expense of bicycle riding, nor do I consider mealtime as dispassionately as if I were just gassing up a car. In fact, I feel sorry for anyone who gets so little enjoyment from their intake of food and drink. I consider any extra food and drink required due to bicycle riding as a benefit and the $ expense as insignificant for such a benefit.

New cost
135
100
20
30
Total $285

commuting expenses
200
100
90
20
40
100
500
100
Total $1150

$1435.00 divided by 50,000 miles = $0.0297/mile

Note: I used this bicycle almost daily in retirement while riding around town, until last year when the rear wheel IGH shifting started to get strange, the bottom bracket was acting up and the bike was looking pretty rough overall Some minor work would get it rolling but I just decided I didn't feel like doing it. As money has never been an issue for when or if I ride a bike, I just retired it to my garage and bought a new 8speed IGH Motobecane from Bikes Direct.