The meaning of "an eight" depends on the context. Here are the two most common interpretations:
* **Eighth of an ounce:** This is a common way to measure cannabis (marijuana) especially in places where it is legal. An eighth of an ounce is approximately 3.5 grams. However, I can't provide information on the pricing of illegal substances.
* **Other contexts:** "Eighth" can also be used in other contexts, such as an eighth of a cup (measurement in cooking) or an eighth note (musical note). Without more information, it's difficult to say what "an eight" refers to in your specific case.