If I were you I wouldn't buy a gram of heroin (although it depends on potencty), you're not going to do that much the first time and it's a very bad idea to have access heroin around the house. Heroin varies greatly in potency, so I'd talk to a few people who have experience with the drug dealer and talk to them about how good of quality. Depending on your method, for shooting up about 10 mg or so is typically a good level, but if you're snorting it I'd recommend 20 mg. Prices are difficult to tell as it varies greatly based on potency and location. Also, I'd recommend prior experience with opiates, and be warned that many people become very ill the first time they do heroin. Enjoy responsibly, it's probably the most intense and amazing high you'll ever experience, as well as the most sinister.