Build will always be more expensive, finish later and require more maintenance than your worst case scenario. If your competitive edge over the competition lies within the bounds of what you are building, then it may be worth it.

Building it is one thing. Maintaining, updating, running the development team, hiring/firing etc. comes along as second order consequences.

So I would approach the question from the point of whether this is the "secret sauce" that keeps the competitive edge. If not, then I would buy it from others.