Exactly. You really need experts in entity relationship data modeling (typically in Oracle DBMS), data hygiene, and codifying business rules. This isn't something web developers should generally take on. Software involving money should consider approximating the formality of engineering approaches: waterfall development model, formal verification, and extensive unit and integration testing. There are hidden costs that edge up TCO for DIY. It's possible COTS maybe very expensive or incapable of being customized sufficiently to meet the needs of the particular application, but DIY should generally be the last resort when no other viable solution exists.