SAP - dedicated system integration (PHP) via BAPI

We are a software house; for our client, we want to implement a dedicated production and warehouse system (PHP) and we need to integrate it with SAP via BAPI. The client is currently working on the EHP7 version for SAP ERP 6.0. The installed modules are SD, MM, FI, CO, PP, PM. Unfortunately, at the moment it is a complete set of information we have, we do not know the number of facilities for possible integration, so I will be very grateful for providing at least a highly estimated valuation of such integration.