Those stations won't cost very much.
From what Metrolinx has been saying, it's looking like a lot of those stations won't be happening anyways. They've really been emphasizing how similar RER and ST are, to the point of saying that SmartTrack is unlikely to perform significantly different than GO RER in their studies. Munro's analysis also throws cold water on the idea of new stations because of scheduling conflicts with GO express trains. We'd be lucky to get a few stations out of this when it's all done.
We should wait until the ST studies are complete before making a judgement. But Metrolinx's comments sound really, really bad for ST proponents.