Vendor Rebate or discount

Hi friends,

My client engage a subcontractor. PO will be create for each delivery sent for the subcon service. At the end of the month, the subcontractor will invoice mu client with the following pricing agreement like below

Quantity per Month Price

0 - 1000 carton $100

1001 - 2000 carton $97

> 2000 carton $95

The PO will be created at $100 per carton.

Is there any way I can setup a condition discount at will check on monthly volume, with multiple POs.

Or can I setup a rebate that will be taken into consideration during LIV?

BTW, I already using rebate with agreement type 1000, for rebate with periodic settlement.