Instead of crap russian equipment why not get a German sub. They have some nice AIP and are clearly in the export market as they sell them to Israel. The Aussies just made a deal with Japan. I am not sure the Japs would trust the Indians with sensitive technology, but they have a common concern with China.
Germany is competing to sell India subs; it already operates Type-209 subs. The French boats are not shabby either (with multiple export orders).