So, how much does it cost to own and run a bike?
Everything I've bought so far£315 for a second-hand Dutch bike
£50 for a lock
£40 for a basket
£0 for lights, panniers (they came with the bike)
£33 per year in service and repairs (It would have been more if I'd got it repaired when it started having problems; it would be less if I had a simpler bike and fixed it myself.)
So in total, this is £400 in initial outlay and £50/year for services and repairs.
Weekly costThis is less than £5/week. This is cheaper by far than any alternative except walking.
It costs £1/week in repairs, and £7.70/week in amortized buying costs over a year. Over 2 years, that amortized buying cost is £3.85, which mine has managed easily. Apparently a Gazelle like mine may last 40 years, which would be 20p/week. But I won't assume that lifespan in my calculations, since London bikes tend to get stolen well before then!
For comparison purposes, then, let's say my bike costs me on average £21/month.
London alternativesAccording to the AA, the cheapest petrol car costs £159.40/month just to own - £43/month without considering buying cost - and that's assuming you never drive it. To that, add between £230-£630/month in petrol, parking, services, and other wear and tear. Owning a car would cost around 20 times as much as owning my bike.
A monthly bus pass costs £81.50. The cheapest, one-zone travelcard costs £93.40/month, and doesn't let you into Zone 1; for that you need to pay £124.50/month.
If you don't use public transport often enough during peak hours to justify the cost of a travel card, then every single journey you take by bike instead of bus or tube saves you at least £1.50.
If I cycle 3 journeys I would otherwise have paid for every week, then owning a bike hasn't cost me any extra.
And everything that is good about cycling - flexibility, reliability, exploring the city, time outside, exercise, convenience, fun - I get for free.