Provence by public transportation

Depending on when you are going, if you have enough time to pre-purchase TGV tickets, they can be very inexpensive. I took the train from Paris to Nice for < $40 and it would be about the same to either Avignon or Arles. For me that amount would make it worth it.

Provence is truly one of the great places in the world, and I'd recommend it to anyone considering a visit. We've been there with a mix of having a car and not having one. The bus system works well, but depending on where you're headed, there may not be lots of buses every day, so that can require some careful planning on the timing so you can catch your bus, both going out and returning. Also, verify where the bus stop for your return trip is located -- sometimes it's across the road or some other place different from where you got off when you arrived in a town.

Much of Provence is hilly, so if you're cycling, be prepared to change gears and crank uphill, and for some exhilarating descents. Some roads are narrow and/or lined with trees right at the edge, with little-to-no shoulder, so use caution, but the local motorists (who aren't tourists in rental cars) will be used to seeing some cyclists. A high-visibility vest would be worth considering.

With only 8 days, I would either fly to Provence and base somewhere there to bike or do Paris -- That is a long expensive way to go to then not be able to move around well because the bus systems are designed for school kids and workers not tourists. Rural France and French villages are just not very accessible by public transit. And with such a brief trip -- that is a long ways to travel for a short stint there.

I went to Provence without a car. I stayed in Marseille, Arles, Avignon, and Aix, and from there took day trips to Nimes (my favorite of them all) and Orange. I could also have gotten to a few other places, but not many, and not so easily.

If these places interest you, you can certainly see them easily without a car. If by "Provence" you mean the rural place with the lavender fields and small villages, you will be much happier with a car.

If you are in decent shape a bike will get you out into the countryside as good (or better) than an auto. But you have to get it the bike and your bags to Vaison, and the weather needs to cooperate.

Many buses change or end their runs in the off season, so check that out first. The trains are a great way to visit places on the rail line (and local trains may allow bikes), but that's not the countryside.

Since you have so little time, consider flying into or out of Marseilles, or taking an afternoon flight home from deGaulle and taking advantage of the express TGV from Avignon. It will deliver you to the airport by 10:30 AM.

If 5 out of 8 nights will be not-Paris, do you really need to begin and end in Paris?

I followed the Rhone and Roman roads this past summer from Lyon to Marseilles without renting a car.
Caught a ride from Arles to Abbaye Montmajour with a kind local gal, but other than that I did fine with train and bus.
If you want to explore villages in the Cote du Rhone, allow plenty of bicycling or bus-waiting time.
RS Provence book has recommendations for Orange and Vaison that are spot-on,
but there are some updated improvements worth checking out in Orange -- there is more than a single story to learn there.
Refresh your knowledge of Albert Belleroche, for example.

If your transport requires Paris, it seems to me that there is plenty to do around there no matter how many times you've already been there!

We happily travelled to Avignon, Arles and Vaison La Romaine all by public transportation. Rick's Provence guidebook has excellent information for navigating this area.

Yes, I would consider trying to do this itinerary exclusively by public transportation to be, as you say, a prohibitive hassle. This is one of those areas where renting a car will enhance your overall experience, because of the flexibility it gives you, compared to attempting it exclusively with public transportation. I would estimate that only about 5% of travelers reporting in here, over the years, have done this area exclusively with public transportation.

The trains are an excellent way of getting to the cities on the train lines, but when you want to explore the country, that's where you're going to wish you had a car.
This part of France is a fairly easy driving experience--but recommend that you be fully insured and that you take the trains to the cities that the trains go to.

Since Paris-Marseille by train is 3 hours, while Paris-Avignon is even less, it's the fastest way to go. There have been several threads on the Forum about traveling in Provence without a car, which you can dig up for some very good information.

Just to second avirosemail's point. If you want to see Paris and Provence, fly open jaw, into Paris and out of Marseille (or vice versa). It may not cost more than round trip to Paris, but even if it does, you'll save time and money by not backtracking (time being especially important on such a short trip). Marseille is a major airport; there are no nonstops to the US, but lots of connections to Paris, Amsterdam, Frankfurt, Madrid, etc.