North West UK, depends on the dealer. Some cheap nasty weed is sprayed with sand, fibre glass, or some other shit - I don't know. But it looks like sand and it makes the bud heavier so they can charge you more for the weight even though there's less product. Usually £20 gets you around 2g of weed, sometimes more and sometimes less. For a full ounce you can pay anything from £160 - £230 up here, depends on the dealer, the quality of smoke, where it's come from and if the dealer likes you or not
Around here, (southern Ontario, Canada) 20$ usually gets you 2 grams, which turn out to be 4 good sized joints, but if hes getting good weed and a lighter 20 sounds reasonable for 3 J's. Enjoy the ganj.