For your setup, you'll need a single adapter as you've already determined. The only real MoCA Ethernet adapter manufacturer I've ever seen is Actiontec. These are the same brand that Tivo sells as well. Since you only need one, the best price I've seen is from Tivo directly. Amazon is currently out of stock, and it's $70 anyways. Tivo's price is $50. I recently purchased the 2-pack of these adapters, but haven't had time to set them up yet. I can tell you that the 2-pack came with (2) short coax cables, (2) short Ethernet cables, and a two-way splitter. I'm guessing the single adapter would come with one of each cable, and maybe the splitter.
Another reason to go via Tivo is they also have POE filters for $9 each. The only Amazon seller is $20. You'll want at least (1) POE filter, and probably (2) to be safe. One is installed where your cable service enters your house. The other might be needed right before the coax enters the cable modem. If it's relatively new, it may have it's own MoCA filter built-in. There is potential for the MoCA signals to interfere with the modem, but I've not seen anyone ever complain of that on this forum.