What is the easiet and cheapest way to soundproof my bedroom door?
My advice would be foam. In Home Depot back in the building materials dept, in the insulation aisle you will find 2 foot by 8 foot sheets of 2 inch thick pink foam. Then in the paint dept you will find double stick tape to install this foam on the door. Once installed it will not add much weight to the door so it will not do any permanent damage. You should be able to do this project for about $15.