How can I record audio & video synced with another audio file? I want to record a drum cover. I have three input sources: a camera, the output of my electronic drum kit (computer registers it as a microphone), and an existing audio file (the song). I want to record myself playing along with the song, and have the resulting audio&amp;video sync up exactly as I was playing it. I'm thinking I want to have a program where I import the song and put it as an audio track, then the program lets me record audio &amp; video while playing back the existing project (namely the audio track).

What's a relatively cheap program that would allow me to do the above? As it is now I have to record the audio &amp; video while I'm listening to the song, then edit the song file in a program to manually sync it with what I recorded, then import that modified song file into the program, which is too much of a pain.
You are over thinking it.  Edit a quick beep in before the audio starts on the song, play the song aloud while you are recording the drums.  Hit one of your drums so that you can see and hear it quickly on the video as well.  Record the audio direct from your drums and have a third track that is the microphone for the camera.  The camera audio track will here both the drums and see the drum hit being used to sync.  Then align the song and the drum track based on those markers in the video editor of your choice.