Do you have to pay for entirely new subscriptions for each receiver for 4DTV at the same location or can you "piggy back" the first subscription?

Don't know, I think it's similar to the way the DBS systems do it, where there is a small additional subscription to support the second serial number.

The thing about C-band and 4DTV is that you can choose different programming providers based on their prices and packaging. There are a plethora of options. I'm with these guys:

http://www.cssnps.com/