Internal PO process

Hi All,

There is a requirement wherein a central team raises  Purchase orders for the business units internally for works undertaken. Here, the amount on such PO's will be 0 (Free Goods indicator turned ON), as the nosiness units wont be charged. But, they need to let the business unit know there was a cost of $$$ for this work to be done, but they don't want the business unit to bear the cost.

What is the best possible solution and process in SAP??

Rgds,

SS