You really have to appreciate how Comcast really tries to sound advanced with "World's First" in the headline.
Assuming the upload will again be 1/5th the download speeds, you're looking at 1Gbps down / 200 Mbps up for a total bandwidth of 1.2 Gbps. That means in a 30 day month you can use up to 388,800 GB of bandwidth. Subtract your 300 GB "courtesy bandwidth" and you're at 388,500 GB over your courtesy limit. At $10 per 50GB you'll need 7,770 separate 50GB "packages" at $10 each totaling $77,700 per month in overages.