Batch specific price determination

Dear Gurus

Our client is having a material milk, for which quality tests are done by quality department. after the test it is decided regarding the payment.

Eg :

PO will be genarated for 100lit with a fixed price of say 15 per lit .

The vendor supplies the material for 100 lit. the GR is done for 100 lit.

but depending up on the quality of the milk the payment is done for a portion of the GR quantity say for 80 lits. Now the system has to propose the lesser price depending up on quality parameters.

regards