From Kawseq Consulting:
An average developer can produce software 10 times as fast as the worst developers. The best software developers can produce software 10 times as fast as average developers. That means the best software developers can produce software as much as 100 times as fast as the worst developers.
1. Hiring cheaper developers actually costs much more up front than hiring the best developers, because you have to hire many more of the cheaper developers to get the same job done.
2. Hiring cheaper developers actually costs more later because you have to spend a lot more developer time fixing the higher number of bugs they put in.
3. Hiring cheaper developers means waiting longer to get working software because of the additional build-test-fix cycles to fix the larger number of bugs.
No matter how much time you give them or how many you throw at a project, cheaper sotware developers cannot produce code of the same quality as high quality software developers. You cannot expect a large number of cheaper software developers to produce a high quality result, just as you would not expect to hire 10 house painters and get them to produce the Mona Lisa. The lower quality produced by large teams of average or poor software developers inevitably leads to software that is more expensive to maintain and develop down the track.
That last bit hits the nail on the head!
Also, cheaper developers do not necessarily supplement more experienced and qualified developers. It just means that the better software developer has to rewrite the mistakes made by the less skilled team members.