South of France Roadtrip advice- with car

I would try to rework this itinerary if possible. Can you fly into Paris and out of Marsailles or Nice? Could save you time and maybe money. Regardless I would take the train to Avignon to rent the car. I usually prefer the villages in provence and find Aix and St. Tropez to be a little bigger and more hectic... I would choose one location (my favorite is St. Remy) and just do some day trips from there. You could spend weeks visiting charming towns and markets, each with it's own unique personality. There is a really reasonable hotel in St. Remy with Van Gogh in the name (can't remember exactly) but it was inexpensive, a bit sparse, but had parking and a pool and was a few block walk to the center of town.
My favorite towns are Vacluse, LaBaux (touristy, but go late in the evening.... views are nice) Rousillion, and a host of others within an hour drive.

Here are a few cost saving tips: Get a loaf of bread and pick up some cheese, olives, and hard salami and have a picnic for lunch as you drive, or pull over for your picnic. Frequent roadside picnic tables along the road serve nicely, and you'll get advance notice of them by the signs with a pine tree leaning over a picnic table. Carry a refillable bottle of water, and top it up whenever possible. At restaurants, get a pitcher of free tap water (ask for une carafe d'eau, sil vous plait).

@Cyn... that is so funny that you mention that sign with the tree tipping over.... I laugh every time I see it...don't they have straight trees???

Is it possible to do you six days in Paris at the beginning of the trip or the end or are those days set in stone because you have already purchased your tickets? If you can rework the itinerary, I suggest that you leave for home from Nice. You don’t say when you are traveling and that would have an impact on which place I would suggest that you skip and whether your $125 per night budget is realistic in such an expensive area. It looks like you are very interested in the eastern part of Provence – the Cote d’Azur – because all of your destinations except Aix-en-Provence are located there. Aix is really the outlier in your itinerary so if I were going to drop one, that would be it. Unless of course you are going during the busiest part of the summer, in which case, I suggest that you drop Saint Tropez (way too much traffic and just too crowded). One thing that is worth mentioning is that a car is not really needed in the Cote d’Azur. For example, you could get from Antibes to everywhere on your list by public transportation.

Why are picking up the car in Marseille? If you want to go to Aix, you can take a direct train there from Paris. Take an early train and explore Aix in the morning and then head to your next destination by car. You could stay in Antibes and be in one of your goal destinations and within relatively short drives of all of your goal destinations (except Saint Tropez) or another place you could stay is Cagnes sur Mer and be short drives from all of your destinations (again except Saint Tropez). If I had 3.5 days and I absolutely had to see all the places on your list and had to have a car, on day one I would take the train to Aix and get the car there and spend the morning and early afternoon in Aix (being mindful about leaving valuables or passports in the car and leaving the luggage properly concealed and paying for secured parking) and then head to Antibes as my base. On day two, go to Saint Paul de Vence and Grasse. On day 3, go to Saint Tropez and if you have time in the afternoon, spend some time exploring Antibes. On the half day, spend the morning in Antibes before flying to Paris.

I'd take the train to Nice instead and forget about Aix for this trip, which cuts your driving time in half and greatly significantly increases the amount of time you'll get to sightsee in the other towns.

Consider one or more of the following instead of Aix:
Menton
Monaco
Eze-le-Village
Villefranche-sur-Mer

I just wanted to say a big thank you to all of you guys for your advice. I got called away for work emergencies that took all my attention from trip planning away, thus I have not booked anything as yet. but I'm close I plan to finalize it all by tonight! Prices are only increasing. I have a lot more clarity thanks to your responses. Unfortunately, we can fly home to Nice directly from the US. That ticket is already bought and is too expensive to change. Plus we have commitments in Paris the Saturday before we leave. However, based on your advice Aix en Provence is not a stopping point. We are only visiting St. Tropez for the sights it will be in and our. We are reconsidering the car rental and might just use public transport to travel through the eastern cities (Antibes, Grasse, Cannes, etc.). I'll keep you posted. Thank you again for your advice.
-Rashida

Also these thanks are address to @TerrKathryn, @cyn @THK and @tecot . @CYN i love your money saving solution, it was already a plan. Thank you