Can I ask what adapters you are using that cost you around $50? Here in Canada I am having trouble finding MoCA adapters that don't cost double that.

https://www.amazon.com/gp/product/B08MQG6T61/ are $99.99 for a two-pack.

Thanks but these guys appear to be quite expensive up here. Cheapest MoCA units I can find on Amazon.ca hover around $163 C$ a pair. However, in the process, I discoved that DirecTV DECA adapters can be used on "dark coax" for $41 C$ a pair. Whoa! They top out at 100MBit/sec, but that would be plenty for my use case. And I just happen to have a fair bit of this "dark coax" running through my house.

Neat hack! If you ever do light up that cable with TV service, remember to unhook the adapters, because they can't coexist with digital cable.

I wonder whether DirecTV engineers approached their management during DECA development and said "we have a problem: this technology we're working on interferes with digital cable," and management replied "uh, yeah, that's not a problem." :)

Most of the mesh APs I've seen on the market also have Ethernet ports so you don't have to just extend the wireless signal around the house. So if OP already had the APs (which it sounds like they did), they just needed to get the MoCA adapters.

Yup, that's what happened. They are $50 each on Amazon US. I think they even included short Ethernet cables, so I didn't even have to root around in the garage to find extras.

FWIW, I got only the 1Gbps speed, rather than 2.5Gbps, because my fiber internet tops out at around 900Mbps and I'm the only one in my family who does anything substantial the local network. For once in my life, I might have enough bandwidth at home.