So here's what I found out about going to the Channel Islands. There are no ferries from Cherbourg to either Guernsey or Jersey. The options from France are St. Malo, Granville or Carteret. All are on Condor Ferries, but Manches Iles Express is also available.
We plan to go St. Malo to Guernsey to Jersey to St. Malo, then Caen and back to CDG for flight home.
Hotels are expensive in Jersey and even more so in Guernsey. We are the kind who favor one-star to two-star hotels or pensiones. The St. Brelades Bay is, as they say in the Delta Dental commercials, out of our network. My eyes watered a bit when I saw the price on the hotel search websites. Looks like we have to schlep over to the Talana Bed and Breakfast.