Before you spend a lot of money, is this a real problem you can hear the effects of, or something that you're reading about and experimenting with? Its easy to go too far and over dampen your room.
Something you can try and will be well worth the effort, is to go and get some fibreglass insulation. Not the stuff that's rolled up, but the kind that comes in rectangular pieces about the size of a picture. Most acoustic treatments are made out of fibreglass and you can use this "cheap" solution just to see if you are headed in the right direction. Actually, many people just cover the store bought fibreglass with cloth that matches the room, and just use those.
