A four day stay in Andaman is not going to be that expensive. You should give a day to Port Blair, Havelock, Neil Island, Ross Island it all depends on what you're lookin for in Andamans but you'll find beauty anywhere you see. Try to stay in a beach resort as it has the gorgeous private beach & is not really expensive. One I remember is El Dorado which is in Havelock Island. Also, do Scuba Diving please. It will cost around 5k per person but is totally worth it. Also, bargaining is the key to cost reduction!!
Hi Vikas, there are plenty of places to visit in Andaman, you must explore the countless beautiful white sand beaches, the cellular jail, Ross island, Viper island, Try your hand with scuba and witness the coral reefs, also Havelock is not to be missed. The budget would depend upon how lavishly are you spending and where are you staying, you can eat decent and stay in a decent hotel with rs.1500-2000/day.
You can spend 1 day in Port Blair, then a day trip to Ross Island, two days on Havelock island where you can enjoy scuba diving, snorkelling etc and then visit radha nagar beach and chidia tapu (where sunsets are heavenly and water is everclear).