You titled your post 'Inventory on Hand Development'.
Since Warehouse Management\Quantity in Stock\Analysis\Inventory Part On Hand Development window and Warehouse Management\Quantity in Stock\Analysis\On Hand Develop per Period window do not show unit costs I assume you  talk about Warehouse Management\Financial Control\Analysis\Inventory Value per Period window.
Here the unit costs are shown per site and period as a statistical value for the particular period.
(Sometimes people talk about Inventory Value per Period window calling it Material Statistics.)

Inventory valuation method selected for the part decides how to assign financial values/posted amounts for inventory transactions. Unit cost at Inventory Part\Costs\Inventory Value get updated upon each transaction which has an impact on inventory value.

‘Aggregate Inventory Transactions Per period’ job will generate inventory statistics based on inventory transactions. If statistics are being updated for an inventory part, the Inventory Value per Period window will be updated accordingly.

The Total Inventory Value in Inventory Value per Period is the sum of the posted amounts for all transactions for the specified part until the specified period.

Unit cost in Inventory Value per Period /Value per Part (calculated as c : Total Inventory Value / Quantity)  displays the inventory unit value per part number for the specified statistic period. This is valid for all inventory valuation methods.