I'm skeptical:

* Where do you buy a ≤20 euro bike?

* Most people on the street have bikes that look to be at least 200 euros new, from what I can tell.

I've never done it, but you buy it from the thief (junkie) directly. So it could be that you find them by word of mouth, like you would use to buy drugs when they were illegal. But you can also buy a second hand bike very cheaply, some are even free (just an example: https://www.marktplaats.nl/v/fietsen-en-brommers/fietsen-her...). New bikes are usually more than 200 euros, dutch brands are 500 euros and up

Presumably from the bike thieves. There's a glut in the stolen bike market so the price competition is fierce.

It seems like that that point the bike thieves are just a bike rental company.

You get the bike for < 20 Euro and then, presumably, at some point in the future it gets stolen again, but you already got 20 Euros worth of use out of it.

"Discount Variable Duration" rental program.

Efficient market hypothesis proven.

Last time I bought a bike for £20 even second-hand, the Euro had not yet been introduced.

Even in 2011, when I made the mistake of spending £90 for a new bike… well, the pedals came off while riding it due to metal fatigue.

Adjusting for inflation*, I'd expect similar build quality from a bike that "only" cost €200 today.

* hard to do when there is also a currency switch, especially when the exchange rate has changed so much

This was 2010-ish and I found one on Marktplaats. Might be going for 40 or 50 now with inflation. People selling them on the street also had for cheap, but these were most definitely stolen.

They didn't mention the year of the story, it could've happened a couple of decades ago.

Police unclaimed bike auctions maybe.

That is rather sad to hear.