How much resources do you reckon would it entail to arrive at such spec?
The thing is, you can't agile this. ERP is notoriously hard to deploy. You have warehousing in ERP, but purchasing in paper? Accounting will love you.
With all due respect, technical software people usually fail miserably at understanding what deploying ERP is. It's by no means software project. The "ERP" could be a huge physical book with all required templates even if very inefficient one, nevertheless deploying such "ERP" would still face *exactly* the same problems.
Deploying ERP is first and foremost business transformation. All ERP deployment horror stories that I have some inside info on always revolve around reluctance of business to transform and instead attempting to contort ERP to fit some undefined shape. Deploying ERP painfully highlights all the spots where business processes are undefined, overlapping or flat out useless. Those processes need to be cleaned up, there's no way around that.
Every information system follows SiSo/GiGo (Garbage in - Garbage out) principle. Humans can apply common sense heuristics and do reasonable things given garbage data. Information systems cannot. That's the beauty and horror of deploying an ERP. If management is actually willing, it's a perfect opportunity to streamline business processes, but if it is managed as some software deployment over existing business - you get horror stories, reduced efficiency and maintenance hell on top.
This, a million times.
Never try to bend an ERP - they are immense business process templates internally connected in incomprehensible ways. Bend the company instead, drop whatever process cannot be implemented trivially in the system and adopt one that is.
Just mapping the parts that need to be transformed is a huge process.
Yes, there are times when processes/procedures are truly unique to a firm but it usually isn’t and the firm can ‘standardize’ their process so that it fits into the ERP flow.
These ERPs are usually shipped to handle common/different scenarios/usecases and clients simply have to configure them accordingly (configuration is totally different from trying to customize)