Car Rental

I would suggest learning about the Cinque Terre in detail to see if this huge effort is worth it.

Why not just take a train to Cinque Terre? There is no "Euroline" train to Aosta. There are only buses and they are seasonal. The train route looks to be about 11 hours with lots of changes. What time of year are looking at doing this?

First, a car in 5 Terre is a waste, use trains. Going to France then back through Valle d'Aosta is a trip. We drove from Geneva to Milan through Valle d'Aosta, great drive as we went through the Mont Blanc tunnel. That was an experience. I think it might be easier for you to get to the Geneva Airport and rent a car there and do the same thing. It is autostrada all the way from Geneva to the tunnel and it is only 54 miles from Chamonix. It is 36 miles to Aosta and a pain to get there.

Train to somewhere that you can get a boat is also an alternative. Seeing the towns from the sea is a good way to get the fell of CT.

I think people may be misunderstanding the OP. The way I read it she wants to get from Chamonix to the CT so she can then spend time there. I do not think she intends to drive between places on the CT or do this as a day trip. She simply wants the best option from Chamonix to the CT.

If this is the case then I would suggest a bus from Chamonix to Courmayeur and then onto Aosta and Milan. From Milan you can catch the train. It will take around 8 hours.

MPH, you are correct. My goal is to get from Chamonix to the Cinque Terre in the shortest period of time, then ditch the car. Once we have turned the car into the Rental car office in La Spezia.
With this being clarified, does anyone have any other ideas?
Thanks to everyone

You are going to an awful lot of trouble to rent a car to cover territory that is served by trains.
Eurolines is a bus company that runs 5 times a week May to September, and 3 times a week the rest of the year.
Savda/SAT runs a daily bus at dep Chamonix at 8:30 am getting to Aosta Bus station at 10:30 am. There is continuing service to Turin Porta Susa train station arriving 12:50 pm. From there a local train to Turin Lingotto at 1:19 pm arr at 1:24 pm connecting to a train to Monterosso departing at 1:39 pm arriving Monterosso at 5:29 pm.

There you have it. A 9 hour journey. Renting a car won't do it any faster.

http://www.sat-montblanc.com/img/os_document/230_chamonix_courmayeur_aoste_turin_milan_31082015_18122015.pdf

Hi Cynthia. Fun idea to go to CT after your RS tour; CT is one of our favorite places. Unfortunately, this is a tricky journey because of the mountains. I would agree with the theme of Sam's recent post. There are several public transit options starting with bus Chamonix to Aosta. From Aosta, I believe you can:
- switch to train for remainder of trip to CT (see trenitalia.com), or
- continue on bus to Torino, catch a train there
- continue on bus to Milan, catch a train there.
- rent a car in Aosta; drive to La Spezia.
The car is unlikely to be any faster than public transit. Also, have you determined cost of the car? With rental, gas, and tolls, it could easily add up to $200 or more vs. 35 Euro each for the train all the way from Aosta to CT.
Anyway, hopefully the more recent posts have gotten you closer to the info you are looking for. Enjoy your trip!