First, only suckers base prices on cost. The companies we're taking about aren't suckers, whether we're taking about Cable companies, isps, or streaming services. Prices are properly based on value. Despite claims to the contrary, Cable television has always delivered value commensurate to the prices it charged even though customers whined about paying.
And value delivered via Cable = value delivered via streaming.
Second, even looking at cost: Think of it this way: Cable television = content + infrastructure. Clearly content = content, so that's a wash. So the comparison is between Cable infrastructure and the infrastructure necessary to deliver streaming services.
Infrastructure = infrastructure. Also a wash.
And after the early adopter bonus dissipates, 5G will impose a convenience premium.
Since we're really just speculating and/or philosophizing here, there's no right or wrong answer. But my math is a little different from the above.
In most places, cable was (and in many, still is) a monopoly, and the entertainment (movies, sports, scheduled TV programs, etc.) it delivered was considered a necessity by many customers. They could literally charge almost whatever they wanted, and the majority would pay. "Value" was not part of the equation.
Every part of that has changed. Customers now have many options for movies. A scheduled TV line-up is almost a thing of the past, as people binge watch what they want, at their convenience. 30- or 60-minute shows are no longer the only format. 6-minute YouTube videos are popular. Customers have lots of options. I think we'll finally get to see where viewers perceive the real value. My prediction is, for anyone growing up in the post-cable era, it'll be nothing like the past.
I think 5G may well be the tipping point for the "ubiquitous networking" previously only found in science fiction. It could become the foundation technology on which everything else is built. The distinction between phone and internet will go away. Costs will be driven by normal market forces, assuming no-one can gain a monopoly, and so should be much less than cable. Not to mention not having to string and maintain wires on poles will probably reduce infrastructure costs dramatically.