How to run the bitcoin client so as to only accept blocks? I read somewhere that running a full node at full functionality requires 200 GB/month bandwidth. Since that is too uneconomical in my country, I would like to run the client such that it simply adds the accepted blocks and does not take part in the rest of the p2p network activity. So is there an option to do that in Bitcoin-Core ?
I believe what you would like to run is an SPV client.  If you are running a full node, such as Bitcoin Core, you wouldn't want to only get updated blocks without transactions.  The point of running a full node is to independently validate the blockchain.  Blocks can't be validated without knowledge of the transactions in them, so full nodes need to receive both blocks and their transactions in order to independently validate the blockchain.  Otherwise, your client would never know if a block contains an invalid transaction (such as more bitcoin in its outputs than inputs).

UPDATE:  As suggested in the comments by Pieter Wuille, the -blocksonly command line option (https://bitcointalk.org/index.php?topic=1377345.0) can reduce the bandwidth significantly.