There's a sign at many (I want to say all?) ticket machines at any LO/LU/XR station entitled "Paying for your journey at this zone x station". I haven't had a detailed look (recently), but I'm pretty sure it includes the cost of travel (Contactless/Oyster/Tickets) from that station to any other zone1-8 station and details about capping and how to use oyster, etc.
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Not sure/don't remember if they can be found at DLR stations; and they're definitely not present (no equivalent) at NR stations.
Having a hard time believing that stations don't display the PAYG fares for common journeys. Surely they must do or this is something they shoul dbe required to do.