With Dutch decriminalized laws on selling "soft drugs" (weed and hashj) the market for it is actually working with competition (most idiotic thing is that growing is still very illegal in NL and actively craced down on by police).
With sales out in the open much about the prices has to do with quality. I live in a city with around 100k population and we have around 10 coffeeshops operating in the area.
Weed goes from cheap: 4-5 euros to expensive 10 Euro's per gram.
Hashj (mostly smuggled from Marocco or Afghanistan) goes for 7 euro's till 14 euro's per gram.
£10 a gram all over the country, sometimes you will get between 1-2 grams for £10 if it is shit stuff. £50 for a quarter is standard if the dealer has a lot of stuff in, and if you want an ounce then you're going to barter. An ounce could be anything between £150-250 depending on the grade and how well you know the dealer.
If you are a frequent customer then you will get more weed. This is true with almost every dealer I've had.
edit: hash is exactly the same price as weed here, though it is typically not great quality.