Amsterdam is bike city. Almost every local has a bike, and I remember there are quite a few places where you can rent one. But - rentals are probably expensive (this answer says 15 EUR / 24h); and I know that you can buy a simple, second-hand bike for 50-60 EUR (eg. on marktplaats.nl). Of course, if you buy a bike there might be something wrong with it, there's no insurance, etc. etc.
So, for a stay of 8 days, is it better to rent or to just buy a bike? And - are there any other alternatives?
PS - I'll only be riding my bike within the city and never out into the country.