If budget is an issue, and you are adventurous, you can fly r/t Paris for much cheaper than to fly into Nice and out of Paris, and take the train to ARLES to meet the ship on July 20. You can come at any time because the ship overnights in Arles. But if arriving before 4pm, you can take your luggage to the ship and enjoy the lounge area or walk around the lovely promenade before boarding officially begins and the group from Nice meets you. When you disembark the train in Arles, just ask where the riverboats are - they'll point you to the river which you can see from the train station - and you cannot miss the ship. It's a very small harbor area.
The train station is literally only 1/3 mile from the ship, and is VERY easily walkable. In fact, Betty DeGeneres and her older sister Helen (who is in her 80's) did this when they came with us a few years ago. We were going to order a cab, but they insisted on walking when they saw how close it was. If they can do it, you can do it :-) Each of them only brought a small wheel-on piece of luggage - traveling by train is MUCH easier if packing light!
Otherwise, if your budget and time permits, I highly recommend coming into Nice, France for the pre-trip - it is a beautiful city, walking distance to the ocean (about 2 minutues) and the flower market is not to be missed!
Jill