with that kind of budget, why limit yourself to India only? it is hard to say who is the best SEO firm in India as I get so many spam mails from so called "leading SEO Company in India" that makes me wonder who is leading whom!
I wanted to go with a firm in India just because they are much cheaper over there, SEO in US is pretty expensive!
India is the best and reasonable cost workers in the world, also it has highest software or IT firm in the world, so i appreciate to you to choose india, but best firm you can search from Elance.com
Instead try to find who is Best Seo company in India, you can hire one or some SEO expert in Elance. There you can read genuine testimonies and see real reputation of SEO providers from all over the world. It is a big chance you can save lots of cash and your project is completed on time. Don't waste your time deal with fake SEO providers that rank high in Google