To get rid of the highs (crack the window and stuff a towel under the door) no, really - some insulation in the walls would be helpful - but if you can't get into the walls, you can put up foam insulation on the walls (4x8 sheets from Lowes or Home Depot - maybe $10 or less each.) - the only problem with that is it's a fire hazard - if you have a fire in your house, the fumes from that stuff will kill ya - it should be hung behind fire-rated drywall. But you can risk it if you want.
To get rid of the lows - it's pretty hard to do - you would have to build a room within a room with a space between the walls (that is, build new walls and ceiling inside your room - so that they don't touch the existing walls and ceiling.) You can put some matresses up against the wall that face into the rest of the living area - and set the drums and the bass amp on a matress -(That would be pretty cool - playing drums on a matress.)
You can also hang foam panels or rugs from the ceiling throughout the room (even in the center of the room) That will absorb a lot of the sound.
There's not much you can do cheaply - but in general, add padding - carpet padding, foam panels, rugs, etc. - and play a lot of oldies so your parents can tap their toes along with you.