I live in NL a few years back, and when I asked a colleage about buying a bike he said: 'just go to central Amsterdam and wait for one of the [slang word for tracksuited petty thief I can't remember] to speak to you. They'll ask you what you want, even what colour, and bring something back within 15 minutes for €50 (or whatever)'.
A downside of everyone cycling there is that bike theft is absolutely rife.