sardinia - by ferry from barcelona to civitavecchia

I don't understand your question about the ferry schedule. If you decide to visit Sardinia, you'll definitely be catching a different ferry departure onward to the mainland. www.grimaldi-lines.com departs Barcelona and gives you a small discount if you have a Eurail pass. To compare other ferry schedules for the second half of the route, try www.aferry.com. See also a recent comment at https://community.ricksteves.com/travel-forum/general-europe/islands-of-the-western-mediterranean.

If budget travel is your goal, then flying from Barcelona to Italy usually cheapest; see www.skyscanner.com.

I'm sure there are a few reasons that Rick doesn't cover Sardinia, including: Mainland coastal areas have lots going for them, and are easier for most visitors to reach for just a day or two. It takes more than a couple of nights to see much of the island. Hanging out on beaches has never been his idea of the best Italy has to offer, when compared to more blockbuster historic cities and art. Some of the more famous beaches and yacht harbors could get expensive and/or crowded in summer. I'd consult a Lonely Planet guidebook for budget-minded practicalities.

It's probably cheaper to fly than to take a ferry from Barcelona to Sardinia. The Spanish low cost airline Vueling has non stop flights from BCN to both CAG and OLB on the island (seasonal, summer only).

Sardinia is a very large beautiful island that is a beach and scuba diving paradise. Historic sights are limited, but there are several quaint villages, such as Castelsardo, that could easily rival the Cinque Terre.

Public transportation options are limited and therefore having a car is really a must, especially if you want to reach the most beautiful stretches of the coast. Most roads are curvy 2 lane highways, therefore it takes a long time to go from place to place. Freeways are available only to connect the provincial capitals and are all in the interior valleys, not along the coast.

Sardinia, being so large and sparsely populated, is never super crowded, not even in August, when compared to many beach locations on the mainland (including the Cinque Terre, which RS loves so much, but that is overly crowded on most days). But of course in July and August, they receive a good number of European beach goers, therefore accommodation prices skyrocket, especially in the most famous locales of the Costa Smeralda. If you go in June or very early July, prices are still very affordable, and food is always reasonable in most places. Actually I find Sardinia (outside of the fancy rich people resorts on the Costa Smeralda) to be significantly cheaper than Sicily and way way cheaper than next door Corsica.

As I said, if you aren't willing to rent a car and/or if you have just a couple of days, I wouldn't bother. What can you see in 2 days other than Olbia and the airport?

Rick Steves does not publicize Sardinia because he loves the place and doesn't want it to share with other Americans, because he doesn't want it to become like the Cinque Terre. Most people don't know that Rick Steves secretly goes to Sardinia every year dressed like a local shepherd in order not to be recognized. You can see him here in one of his recent camouflaged trips to the island.

Thank you for all the advice! it was very helpful!