Based on prior knowledge, the relationship between the feature "buying price" and the task "decision to buy this car" can be analyzed as follows:

- Very High buying price: It is likely that the decision to buy the car would be "unacceptable" as the cost is too high for the buyer.
- High buying price: The decision to buy the car could vary depending on other features or factors. It is possible to have a mix of "acceptable" and "unacceptable" ratings.
- Medium buying price: This could result in a mix of "acceptable" and "good" ratings. Some buyers might find the price reasonable, while others might consider it too expensive.
- Low buying price: Generally, the decision to buy the car would be "good" or "very good" as the price is low and affordable.

Based on this analysis, the dictionary can be created as follows:

```json
{
	"unacceptable": ["very high"],
	"acceptable": ["high"],
	"very good": ["low"],
	"good": ["medium", "low"]
}
```

Note: "high" and "low" values are included in more than one target class as they are likely to be ambiguous and could result in varied responses.