"Worth" is in the eyes of the collector. I did find this "completed" listing on
ebay for three examples listed a few days ago, including one with the same postmark as yours. They were originally listed for $41.99, then lowered to $25.99 with starting bid at $15.99, but alas, no sale -- even with free shipping.
I have no idea if there's any source for those numbers or if they were merely created by the Seller, but with no sale at $15.99 (about $5.33 per cover), I can only imagine that demand for them must be quite low and/or they are overpriced even at that minimum bid amount:
http://www.ebay.com/itm/1965-India-...047675.l2557