I would say, firstly, from the figures I've seen in the Obama budget, that the climate change revenue--as I recall, that's their term in the bill, “climate change revenue”, so you'll have to discuss with them whether they consider it a tax or not--is estimated in the year 2012 to be $78.7 billion.
I've only seen reference to the $300-billion figure as...issues that some economists have taken with the projections in the American budget. They've said it could be double or triple what the President assesses.