20 dollars worth of marijuana. depends largely on the quality. very low quality mexican schwag can be 3 grams for 20 dollars. high quality stuff on the street is generally 20 dollars per gram. at 275 dollars an ounce, which is about standard, it comes out to a little under 10 dollars a gram. Most dealers are willing to sell a gram for 15 dollars, or about a gram and a half for 20. It depends a lot on the dealer. Many street dealers here in berkeley will actually sell 3/4 of a gram for 20 dollars (see "custie").
i have also heard the phrase "dub for 15", meaning selling what would usually be 20 dollars of marijuana for 15 dollars.
"I came across 25 dollars while cleaning my room, so I bought myself a dub sack, some phillies, and a lighter"