To assign costs to specific storage depending on the tier requires two operations. You must define the cost levels to the Tiers and you must assign the datastores to the tiers.
To assign the costs (as seen in screen shot below) you need to go to “Policies”, “Virtual/Hypervisor Policies”, “Service Delivery” then select the “Storage Tier Cost Model” tab. Once there select one of the four Tiers and click on the Edit button; repeat this for the other three Tiers. Notice the costs will display on the fare right for each Tier.
To assign a specific Datastore to be a Tier (as seen in screen shot below) go to “Virtual”, “Storage” then select the “Datastore Capacity Report” tab. Once there select a Datastore and click on the “Assign Tier” button. This will bring up an additional dialog box which prompts you to select one of the four Tiers. Repeat this operation as need for each of the Datastores you wish to apply a storage tiering cost model. Notice that the column “Storage Tier” will now show which Tier a given Datastore is assigned to.