Interfacing is typically 4x the complexity with less return.
Oracle ERP is the most flexible for custom configuration and programming. It took me only a week to get productive with a PLSQL book (many years ago).
The basis of the issue seems to be lack of standardized business processes. What you face isn't a technical issue, but a functional issue of business process re-engineering for the company. The other is a good change management process.
The other issue that I see is Atlanta because it's probably the most in demand of skilled ERP developers in the USA right now. Try other cities for your development teams. I can think of a couple dozen cities where I can find skilled software engineers with 10+ years experience in the $100k range - they are typically 4x to 10x more effective than new hires.