When i returned to cycling some nine years ago I bought a bike, riding kit for all weathers, tools, spares, modifications for the bike, another bike.....
Now after having to change from two wheels to recumbent three due to balance issues, I haven't bought a trike for over a year and don't expect to buy another anytime soon. My last big spend was for different brakes on my newre trike, before that it was new tyres for both my trikes last winter. Two were worn out on my older trike, three on my newer trike were cutting up very, very badly in the cold weather and I bought a spare.
I fully expect to not need any more tyres, or brake calipers (disc brakes) for some time and will need to replace the pads on the new calipers some time next year.
You can ride one bike only and will find the running costs come from, in no particular order, tyres and tubes, replacement chain, eventually replacement chain rings and cassette, brake blocks, the odd cable, brake or gear and wheels. You won;t need to replace everything at once and some basic care particularly to the chain will put off replacements for a long time. Some people get a few hundred miles from a chain, I get 2500 miles plus and replace it then to avoid wearing out chain rings and cassette. My commuter bike, I'm retired now, has 10000 mles plus now and had 3 new chains, and new wheels a few hundred miles before I found out about my balance problem and stopped riding. It still has the original cassette and chain rings and the last time I changed the chain there was no discernable wear to the teeth on any sprocket.
It cost me £900 new, the wheels were under £100 for the pair, from the makers and identical to the originals chains cost me around £18 each and I've replaced the brake blocks once from new, the original tyres are in excellent condition and I've had some replacement tubes as I don't trust a patched one.
So total cost is under £1200. That works out at 12p per mile.
My car costs that in petrol and then there is Tax, insurance, servicing, buying the thing, servicing, (I service my bikes myself but leave the car to the garage).
Also I enjoyed nearly every mile on my bike and drive because I have to!