I cannot provide figures but I would warn against under-estimating how much time this will take. I have experience of developing SharePoint for another regulated document management system in a previous role and the effort was huge (development cost in excess of £50k 10 years ago).
I suggest taking a look at the GAMP5 requirements, if you’ve not done already, to identify what you would need to have in place. You can then start to work out how much effort this will take. You will need as a minimum:
– User Requirements Document
– Functional Requirements Document
– Validation Plan
– Approved Test Scripts
– Executed Test Scripts
– Validation Report
– Change Control Procedure
– Maintenance Procedures/Manual
Of course, you will also have to maintain the validation status of the system over time, identifying what updates Microsoft have made and the impact on the validated system (repeating validation where required periodically).
If you are archiving regulatory documents using SharePoint, you will need documentation that describes how you intend to maintain the accessibility and legibility of the content over the whole retention period (likely to be 25 years) i.e. a digital preservation plan.
I think this is why the trend is for sponsors to purchase an off-the-shelf system as it can reduce significantly the amount and cost of validation activities. An apparent cost saving in the short term by use of home-built SharePoint is likely to be more expensive in the long run.