Where can I purchase a Digital TV Receiver for another TV in my house?

I recently purchased Digital TV service for my house. Only one room has it but I want it in the bedrooms and didn’t want to pay AT&T bundles of money to connect it. Where can I purchase a digital TV Receiver and is it difficult to hook up? Anything I should be aware of?

If you want all the channels AT&T offers you have to use one of their boxes. If you buy one on ebay or something, AT&T won’t activate it, so you’ll just be wasting your money.