You need an expert db designer to begin with. A small database (50 tables ballpark) takes around a month. A 50 tables addition to a 3,000 tables database on the other hand may take 6-12 months.
Beside the expert db designer, excellent systems analyst is very very helpful.
Funding and ROI is just like any other software project undertaking.
A good database design pays off tremendously in development productivity and ease of maintenance.
Kalman Toth DB, DW & BI Architect, SQL Server Training
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