Barack Obama's presidential campaign is getting a bargain for the half-hour of Oct. 29 primetime it's bought on CBS and NBC. The Democratic presidential candidate's camp is paying under $1 million to each network to run the programming it will produce for the first half-hour of primetime that Wednesday night, less than a week before the election. This is considerably less than the networks would otherwise get for the 10-11 ad "units" they run during that half hour, between 8 and 8:30 p.m. Obama is not getting a price break; the campaign will be charged what's called the "lowest unit...