Rent an Scooter or Bus to explore the iland.

We are here now and have been to both. I’d pick Perivolos. Cool boardwalk strip with restaurants, beach clubs and pools. If you eat at one of the restaurants that has a pool you can swim. Also beach is wider and a bit nicer in Perivolos.

There is some white sand near "Red Beach" . Red Beach is officially closed, but you can still get to it. There's also a beach called White Beach, but I think that the name has more to do with the cliffs behind it than the sand color, but there may be some white sand there. However, the black sand beach at Perissa is beautiful and soft, not pebbly like most volcanic sand beaches.

si, si può arrivare, ed una volta li consiglio di fittare una macchina a perissa( ci puoi andare a piedi) per fare un giro dell’isola

There were some people snorkeling. We did snorkel for a little bit. There is not much to see but little fish here and there.

We used Santorini Experts for our cruise tour. They customize the tour to your wishes. I'm sure they can take you there.

You can find something within 15 to 30 gbp. Don't get too big a car, get a small economy one: roads are small, you'll never be able to go more than 70 kph. Buses work well if you're on a budget, but you won't be able to get to the more remote places. You also have the option of scooter or ATV. It's my 2nd time on the island and I would still only recommend a small car. The sun hits hard, so you need the protection or you will roast, but still roads are small and crowded, better a small car than a bigger one. This recommendation goes for the mid-September period. I can easily see this place be a total mess with summer crowds.

Rental cars are very inexpensive, grab one in Fira and it is 20 minute drive. Well worth the drive and you can come and go to the beach as you like. There is plenty of parking everywhere and parking is free.

There are car hire companies at the airport, which it is probably better to book. I organised this online. But I noticed many car hire companies around . There are also quad bikes to hire which a lot of people do.