Yakushima bus cost from airport to Miyanoura

Hi all,

I'm brainstorming a trip to Japan wither a friend later this year, and plan to stay at Yakushima for 3 nights. The current plan is as follows:
Day 1 - Fly to Fukuoka in the morning from overseas, then transfer to a flight for Yakushima which should arrive around 4pm, then head to Miyanoura
Day 2 - Shiratani Unsuikyo hike, perhaps Environmental Village Center
Day 3 - Rent a car in the morning, and take a road trip around the eastern and southern part of the island, particularly for waterfalls and maybe Yakusugi Land
Day 4 - Take morning flight out to Kagoshima

A few questions which you guys may be able to help with:
1) What is the cost of a single bus trip between Yakushima airport and Miyanoura? I'm guessing bus passes won't be worth it for that single trip.
2) I know the bus between Miyanoura and Shiratani Unsuikyo are infrequent, and that an alternative is to rent a car for this as well. Does anyone have any recommendations for which might be better from past experiences?
3) What would be the cost of a single bus trip between Miyanoura and Shiratani Unsuikyo for that matter?

I can't answer your questions off the top of my head, but the Yes! Yakushima website is probably the best place for you to look. I got the bus timetables from them when I did the Shiratani Unsuikyo hike in November 2014. However, I went straight from the airport to the hike, and then back at the end of the day, so I bought a bus pass and not single tickets. The buses were easy to use, though, as they would tell you to get off at an upcoming stop if you wanted to access a certain area (hike/airport/Miyanoura).