A RSA token generates a one-time password based on the timestamp and a private key using an AES algorithm.
RSA tokens usually don't have any encryption inside. They are only used for authentication.

The nano s is a hardware wallet which is capable of signing different transactions using different signing algorithms and addresses.
Additionally it gives you the opportunity to check the details on the screen and confirm via buttons. It has a smart chip built in and the seed stored encrypted inside.
The Fido U2F application is comparable to the RSA token.

There are quite a few differences between those two products which justify the price of the nano s.