If you have bodybuilding goals then peanuts won't work as a *primary* source of protein, because they still derive 65-70% of their caloric value from fat. As a normal source of dietary protein for everyday people, though, peanuts are excellent.
Dude though! If you want an even CHEAPER source of protein -- one that's available EVERYWHERE in India -- then go with LENTILS!
Lentils get about 30-35% of their calories from protein (versus peanuts, which only get 15-20% of calories from protein).
And you can buy 5 lbs of lentils (= 2.2 kg) here in the US for less than $2. That's about 600 GRAMS of total protein.
In India, I'd imagine you can buy 2 kg of lentils for, what, probably US$0.50 or less?
I love curry, so I wish I had a bag. Please, may I smash your face! Wait a minute, I didn't type that! My right forefinger, fell out of my left nostril, and insulted you. I apologize on its behalf. (Have you seen the inside of my nose?)