I'm also going into Amsterdam around the same time (JUN 7) and I have found that its rather difficult to find anything under 100 dollars a night. You may want to try looking for bed and breakfasts in Amsterdam. They seem to be relatively decent prices and may still have openings during your four day stay.

Whatever you do, have fun though!
Roger

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Roger travels to Europe this summer. Follow along! http://www.thisworldtraveler.com