Did you read that it was for a stag do and as cheap as possible...the hilton all the way
makes the visit all the more special
Go to the coffee shop where its full of grapheti (sp). At door coming out of the place turn left go along there but cross over path, and keep lookin at the buildings to ur right, there's a place there that was 30euros a night and was comfy, had key cards for security and breakfast in the mornings. If i was going to the dam id go back there.
Get a house-boat, so much better than staying in a hotel, you get a space that's yours to do what you want with for the stay. Though this will depend how many of you there are of course, most of the cheaper hotels i've stayed in in Amsterdam have been pretty dire so can't recommend any of them really.
Bulldog cafe?