The problem is that, again, the only team who has the resources to offer 20 per for a pitcher are the Yankees, the Mets, after they sign one of Holliday/Bay (and they will) won't have the money either, also, remember that teams have the leverage to negotiate with him a longer contract that pays him less AAV than Halladay, because he simply shouldn't be paid more than Halladay or Santana, because they're much better, and it's not the Yankees we're talking about.
The point is not the 100 mill, it's the 20 mill AAV. In the contract scenario you just posted, he would make 18.5 annually, not 20, and also, i highly doubt he gets 6 years guaranteed unless a team is really desperate.