Amsterdam is a tourist town and has a wide variety of hotels and room prices. We have not booked a dedicated block at any given hotel. Hotels along the main canals will typically be more expensive, but reasonably priced hotels can often be found in other places (e.g. near the Museumplein or Vondelpark, for example).
The workshop venue is located just behind Amsterdam Central Station, thus any hotel in the centre which allows easy access by walking or public transportation to the Central Station will likely be convenient. Many of the trams and buses running through the centre originate from the Central Station, and thus are typically only a small number of stops away.
Note that because 25 May 2017 is a holiday in much of Europe (Ascension), the weekend after the workshop (25-28 May) is a long holiday weekend and prices might be somewhat higher.