A great developer can be 10 times as productive.
In creative professions, that difference between the average joe and an expert can be huge.
They can be the katalysator to your project. They can be like magic.
This is so hard to grasp for managers, but I have seen it happen a couple of times.
I was in a team with two exceptionally good analysts/testers and two very senior developers. We outperformed any other team in the company in the last 5 years.
Outsourcing seems logical on paper. In India, the developers are three times cheaper. But if you don’t realize that some experts have a special multiplier, you will go wrong in the math.