Cost: the hike itself is for free. Only cost are for transportation.
Personal opinion: This was the best hike in Madeira. It had everything: stunning views, solitude at the beginning of the hike, adventure during the tunnel crossings and an amazing end in Calderao Verde.
If you every have the chance to visit Madeira take the time to hike to the Caldeirão Verde. There is also a shorter hike (round trip) from the car park possible.
Pingback: Madeira: What a view (Levada do Rei) - Outdoor Sandra