An interesting article in Cableworld about the difference between Broadcast Network and Cable Network advertising rates. Among other things, Cableworld points out that cable advertising CPM's are half that of the Networks in prime time...
"According to Nielsen Media Research's Monitor-Plus service, which measures ad spending in all major media, buyers spent $21.10 to reach each 1,000 viewers in the key 18-to-49-year-old demographic (called cost-per-thousand, expressed as CPM in agency jargon) during prime time on broadcast, compared to $10.60 on cable."