Requisition with estimated amount and quantity, but NOT price

Hello Gurus, Cient would like to create requisitions from iProcurement with a total estimated amount (header level). We know the quantity items (quantity lines)and the estimated amount for every requisition, but not the price lines (this data will be know the the RFQ or PO). Furthermore the estimated amount has to be  requisition encumbrance.

If you could please share your experience, or which combinations of Oracle modules can allow to perform this requirements.

We are on Oracle 12.1.3

Let me know if any good reading material is available.

Thanks a lot

Regards

Verónica