I think this is correct right now, but the biggest cost by far for generating green methane at scale would be the energy costs for electrolysis to get the hydrogen from water. If renewables continue to fall in cost, we may rapidly reach a point where we have a huge surplus of green energy for parts of the year. There are already places in the US where energy prices regularly go negative due to excess wind energy, for example.
Folks have talked a lot in the past about using excess energy from renewables to generate hydrogen gas, but hydrogen alone is a lot harder to manage, is much less energy-dense by volume, is impractical to liquefy for storage and transport, and isn't compatible with existing infrastructure. Methane solves all of these issues, and doesn't take much additional energy to create beyond what you must spend for hydrogen alone.
1 https://spectrum.ieee.org/energywise/energy/batteries-storag...
And if you use a methan fuel cell - you can use its surplus heat for heating while generating electricity.
I don't think they are market ready, though. But there are lots of options out there and the best solution is likely to combine what works now.
Btw. I think there was a breakthrough with natrium based batteries. (No lithium needed). They were just not as energy dense as lithium based ones, but that matters not so much for stationary use. So with no ressource limitation, you could produce them in very big quantities..