Once you have a decent number of potential customers in a small area phone the content providers and find out how much it is to license the channels.
If you're still profitable you'll then need to estimate costs for building out your headend, source a location for your satellite dishes, call centres, etc. Find out costs for this. A lot of cable companies, especially Rogers in Canada outsource a lot of their infrastructure / install work, you should be able to find out from their builders rough estimates of build out costs.
Write a business plan and then find out if you can find someone to fund it. When you find someone to fund it, go build it, then sign up your customers.
But seriously the trick to this plan is to figure out how NOT to build out cable infrastructure, I'd look at piggy backing on LTE / Internet in the same way that hulu/netflix/youtube do.
You'd be far better off spending $50 million figuring out how to build synthetic aperture recievers / transmitters and figuring out how to transmit data over the wifi spectrum within the power limits outlined by the FCC rather than building $50 million in 1990s cable infrastructure.