Hi,
We had no trouble getting a taxi from the ship to Avis. It couldn't have been more than a couple of miles by cab.
We also had no trouble navigating around Normandy, and went as far as St. Marie Eglise. The roads were generally good, partially toll roads and bridges as I recall.
We looked into getting a personal tour guide, but they were pretty pricey. Our cruise tablemates took a ship tour and we beat them to Omaha Beach. And then we saw much more than they did. We ate lunch at the Roosevelt (Teddy, Jr.) cafe on Utah Beach.
You can do it yourself and have a better experience in the process. The viamichelin website provided good maps, and some of the other Normandy websites showed us what to look for.
Regards,
Dick