For every dollar a good Indian firm makes, the average developer gets anywhere between 50 and 80 cents. Good devs are equally expensive anywhere, but oddly enough in India the salaries don't grow linearly when compared with first world salaries. A dev with a year of experience will cost 1/5 what he/she would cost in the first world. A (good) dev with 15 years of experience would cost 1/2 what he/she would cost in the US.

This was something we covered in some detail in our talk at Rubyconf last year. Here's the link FWIW: http://speakerrate.com/talks/5120-india-ruby