I bougth a second hand bike for 40eur 5 years ago, and I only had to fix the wheel once (5 eur). Never had to buy clothes, special locks or anything fancy... I use it daily...
Unless you live somewhere with a great climate, foul weather clothing inevitably ends up needing bought if you intend to commute all year round by bike.
I spend about €15 a month on my bicycle if I spread out the cost of purchase, clothing, and maintenance (mostly parts, I do my own maintenance, which isn't uncommon here). That's for a high quality, extra tall bicycle (I'm 2m tall) that looks presentable enough for my daily commute to work.
A student could probably manage with €3 to €8 a month.
That said, you're now making me curious to what degree this applies to other cities, even just cities that are known to be bike-friendly. In how many cities is it normal (or even possible), like in Holland, to use bikes in this ways?
The style of bikes that are popular in Amsterdam and other relatively flat European cities often aren't that commonly found in many other countries in my experience - the incredibly popular in Holland 'coaster' brake design (where you stop pedaling/pedal backwards to brake) is borderline dangerous on very steep hills, but works great in flat areas, making it pretty uniquely suited to cities like Amsterdam. Similarly, you guys rarely need to bother with gears, or need so few you can use much simpler to maintain hub gear systems rather than finicky external derailleurs. I've almost never seen a new bike sold in the UK with coaster brakes, largely due to safety on hills. Similarly, it's pretty rare to see a coaster brake equipped bike in the US. I sure wouldn't want to try stopping at the bottom of a long 30% grade in San Francisco on coasters...