We were in Amsterdam four years ago without a hotel reservation and were able to book the Amsterdam Hilton through the VVV (Tourist Office) at a rate of 100 Euros. Breakfast was not included. We had to pay about 20 Euros for parking since we had a car; we had to move it from the park and go lot where we had parked for the day.
We were excited because it was where John Lennon and Yoko Ono had their "bed-in" and we even stayed on the 7th floor - the same floor that they stayed on.
The hotel was quite lovely. Our room was wonderful. We had a gorgeous view.