Why stay in a sterile airport hotel when you can stay in a nice, little hotel in a real town, say Mainz (the capital of the neighboring state)? By S-Bahn (rapid commuter train) it's only 26 minutes (no transfer) from the airport to Mainz main station. And Mainz has lots of nice restaurants serving real food, rather than hotel restaurant food. The same S-Bahn continues on to Wiesbaden (capital of the state that Frankfurt is in), only ten minutes further and a bit more elegant than Mainz. The internet has lots of hotels in these places. The trains run every 15 minutes or so.