RBS2.0 satellite

As the Netgear page shows, the only Orbi satellites compatible with the original WiFi5 systems are the original WiFi5 satellites.  None of the Orbi WiFi6, 6E, or 7 satellites are compatible with the original routers.  The original WiFi5 units can be purchased used on eBay and "renewed" on Amazon.  (Several years ago when I realized that the warranty had expired on my WiFi5 Orbi router, I purchased a spare router on eBay.  Haven't needed it.... yet.  Maybe never will.)

With the limited supply of original WiFi5 units, they are definitely "not cheap".  It is sometimes less costly to purchase a new WiFi6 mesh system for less than the cost of a single used WiFi5 satellite.