That's really not much of a cost though. Even if they have to install a new dish and run coax to several rooms it is under $100 in materials. A couple hours labor is maybe $100, plus let's call it $50 for the truck, gas, insurance, etc. If it is a house that's had Directv before the dish and wiring is good, the visit is pretty short and probably costs less than $100.
The cost of the receivers is irrelevant, because that is WAY more than paid back by the $7/month fee - with a five year depreciable life (and a lot of equipment ends up being used longer than that) that adds up to over $400 which is more than double what it costs them to build a Genie, let alone a client. If you consider that $250 cost over the two year life of a commitment, that's $10 a month - a lot more than the difference in price between Directv satellite and Directv Now.
Now before someone brings up the ~$800 "new customer acquisition cost" most of that is paying for the ads they are running on TV. The need to advertise doesn't go away just because you are selling streaming rather than satellite. If anything they will need to advertise more, because there are more options and the pricing of their competition is a lot more cutthroat.