Does it blow out cold air, or does it just not blow any air? It if blows, but it is just cold air, check your coolant level. It is possible that it is just low, and you might get off easy. Does the temp gauge read the the engine is hot? You might have a line clogged going into the heater core.
If it isn't blowing any air at all, it is likely the blower motor.
Do you hear a fan-like sound, or nothing at all? If you don't hear the fan, then it would be the blower motor. If you can hear the fan trying to blow the heat, but nothing comes out, it is probably a vacuum line. Does it work if you put it on a different setting? What about the AC?
Heater core bypass...I did it for a while until I got around to replacing mine when it busted. On a similar note...antifreeze smells worse than rotten ass on an 80 degree day while it's sitting on your floorboard from a busted heater core.