Put a bullet in the bastard, throw the camera in, bury him 6 feet under.
I also know a couple of russian friends if your trigger finger is a bit on a weak side..
Just kidding.
But seriously,
For ghetto coffin, get some 2x4, wrap it around an actor, shoot with super wide lens. You just need the head shot, of him looking up. Wouldn't cost more that 20 bucks to build 3 short walls, 2 feet tall, 3'5 feet wide.
For a fancy coffin, you've got to decorate it a bit. but shoot the same way, from bellow super wide lens. Use 60watt light, super defused.
Make him look at his feet, cut the scene, where you flip the dude other way around, and shoot his feet the same way.
Make sure your audio is super dry and non echo'y. Audio will sell the effect.