Buying Air Tickets Online for chennai, Trichy, Goa, Mumbai

I would like to know if I can expect to easily buy inexpensive airline tickets between Chennai - Trichy, Chennai - Goa and Goa - Mumbai one or two weeks in advance while I am in Mumbai. I live here in New York and from my computer here in the U.S. apparently I can only buy tickets with Jet Airways and Indian Airways and it seems like the tickets are all at least $100. Won't they be less expensive while I am in India and at the time I am there (in late October and early November) could I expect there would be availability? I certainly can't find a way from here in New York to buy cheaper tickets with Air Deccan or Sahara Airlines. If anybody knows a way I can do this or have any advice on how to get airfares while I am in India, I'd really appreciate it. I am afraid that in late October and early November I may get there and there could be no more availability.

Oh, and also, what does NRI stand for ?

Greg in New York

They wont be any cheaper based on your locality and will probably increase in price closer to the flight date.
NRI = non resident indian

Deccan and Sahara both have online facilities.