I want to ship some books from US to India. They would weigh around 30lb. I heard from someone that USPS has a "shipping" option which takes long
but is very economical... but I don't see it on their website. If anyone knows whats the most convenient shipping option please share.
Given that that URL includes ".../senditwithintheus/..." it's probably a safe bet to assume that it doesn't apply to your situation. You may be thinking of M-Bags: http://www.usps.com/international/sendpackages.htm
Alternately, you might be thinking of surface mail, transported on a ship rather than an airplane. Unfortunately, USPS eliminated this option a couple years ago. I'm not sure why.