That's a lot of it. The AC3 plug-in doesn't work out of the box - you have to register the plug-in online first, so that's not included in the overall price. Same with the MainConcept MPEG-2 encoder.
"Does Vegas do a lot of tricks, like doing the proper phasing when you spread your additions across channels?"
Good question. I'm not sure. I'll get back to you on that one.
"6-channel PCM? Do players do 6-channel PCM? I'm out of my depth, here..."
Not to my knowledge, but considering how much space such a soundtrack would take up - WOOF! In fact, if I remember correctly, when I made a 6-channel PCM soundtrack, my computer wouldn't play it (it was an intermediate step in turning a 2-ch PCM track to a 5.1 soundtrack.)