I think anytime you activate a new receiver you have to sign a new two year contract.
It's basically like a cell phone. A new Iphone 4s is not $200 alone. Your basically giving $200 for the device, and signing a contract which means you promise to pay them for the next two years.
Of course, a small portion of your monthly bill goes towards the device cost.
Now with Directv, a HD DVR is $199 (price is for the sake of argument).
Let's say full price of the HD DVR is $600.
Well when you pay $200 for the device, your contract says you will pay Directv for the next 24 months.
So for grins and giggles, $16.66 dollars is taken out for your bill each month for the device cost. Which equals $400 for the 24 month commitment.
I don't know much about sales, but I believe you can get up to 4 rooms free, so it is best to get all needed receivers at the time of signing up as a new customer.