Well Ive done a bit of research and had some feedback from members on this board (Az has been there recently), and I know for a fact that if you go during the Cannabis Cup the prices are 'hiked up' considerably. I dont know by how much, but its supposed to be quite expensive for food and drinks, plus during the CC they put the prices of bud up in the coffeeshops.
Im actually thinking of visiting a small town instead of Amsterdam. As long as it has its own coffeeshop though