You can specify that your price attribute has an apriori order. By doing this there is no need to ask the rating question for price since it is already known.
Importance questions are designed to guage how important an attribute is compared to the other attributes. You already know that lower prices are more desirable, but how important is the difference in price compared to the other attributes?
You can choose not to ask importances at all, which will internally mean they will all be considered equally important. If you only ask a subset, it is impossible to determine how important the other attributes are in comparison.