To look backward for a while is to refresh the eye, to restore it, and to render it the more fit for its prime function of looking forward.
Margaret Fairless Barber, The Roadmender
Network Tiers - Comcast organizes the various networks into 3 tiers, with tier 1 networks being the most popular and consequently the most expensive to advertise on. An ad placement in the South East area during the 6am to midnight time frame (which means the ad could run anytime in this time period) on a tier one network typically costs around $6/placement - other time frames (such as prime time) are more expensive.

Tier 3 Networks
One thing to keep in mind is that tier 3 networks cannot be sectioned geographically, but instead cover the entire Denver metro area; consequently, while Tier 3 is the least expensive per subscriber, because you have a larger subscriber base (the Denver Metro area) the actual per ad cost may be higher than tier 1 where a specific area ia selected.

Read more about Coverage

Read more about Costs

Tier 1 Networks
 
Tier 2 Networks
 
Tier 3 Networks