Reliable uber or car service from Rome Airport to Castiglioncello?

How many is "we"?

It is 260 miles, so 500 EUR might be quite a bargain. On the other hand, you could go by train for 28 to 35 EUR per person.

As Sam mentioned, the distance is considerable (not quite 260 miles, but probably 260km). Nevertheless it’s a 3+ hour drive, one way, therefore I’m sure the car driver wants to be paid accordingly.
I would either take the train, or, if you want to have a car there, you can rent one at the Rome Airport.

There are 3 of us, possibly 4. The train times are not good for us, so that is why we thought a car service would be good. However, we might have to rent a car.

How difficult is it to rent a car at the rome Aiport and what is required for one of us to be a driver?

How difficult is it to rent a car at the rome Aiport and what is required for one of us to be a driver?

Probably no more difficult than at any other airport of comparable size.

Valid drivers license, International Driving Permit (IDP) and credit card, are the needed basics. A GPS of your choice is helpful and reading up/learning the traffic signage, ZTLs and a disposition to adapt to different driving styles are helpful.

You get the IDP at AAA, photo can be taken there too. We have a Europe map chip for our Garmin GPS.

Thanks so much for your assistance and information! Much appreciated!!

If you have never driven in Italy, please read this and download their PDF. Lots of important info for driving in Italy.

https://www.italybeyondtheobvious.com/dont-mess-with-ztl-zones

Since you're already at the airport,
You might also consider flying to Pisa (1hr ) and renting a car or taking the train from there.

Alitalia has several flights a day.

Definitely get an International Driver Permit. It costs $20 and you get it at any AAA office. You won’t need it to pick up the car but if you are asked for it by police and you don’t have one, you can be hit with a hefty fine in the €300 range.

Reserve a car before you leave. Suggest you check with AutoEurope, a consolidator in Maine that’s highly recommend on this site. Great prices, excellent customer service. Also recommend getting a car with zero deductible insurance. Note that your credit card will not normally cover insurance in Italy.