How much money should I spend for a 4 day weekend in Amsterdam?

How much money should I look at spending (in American dollars) for a 4 day weekend (actually 6 days - 2 days flying - one there, one back - 4 days actual time in Amsterdam). I have never been there before and would like to hit the Heineken Brewery and Van Gogh Museum. Hit as many coffee houses as I can and eat out only once a night. Of course there will be beer, weed and snacks during the day (or night). Sorry but I am trying to be detailed because I am sure one of you out there has done this exact type of trip, or pretty damn close to it! Also when during the season is the air fare usually cheaper? One last thing I do not have a pport. How much will that cost me? Thanks a bunch in advance for any answers!