Team with the customer use the Bang-for-the-buck technique to rank the work items based on the value of each feature and the required estimated effort for the development (cost).
The team knows the size of the work items best, and the customer knows the business value of the work items best.
When story points are used in the bang-for-the-buck technique, the benefit value of a work item is the division of the value points by the corresponding story points.