We were sceptical about going to the rain forest of India in monsoon but believe me , the moment we step our foot in kerala, we knew it's going to be amazing. Air fair to Kochi in monsoon is fairly low and it was one the reasons to go there in monsoon. Since we planned to go to munnar before anywhere else in kerala. We took a one way (goibibo) cab to munnar which cost us around 1400 ( fair enough ) . From Kochi to munnar it takes around 4-5 hrs depending on weather and time of travel. We reached at our prebooked hotel at Ananchal at 9 PM.
Tip: If you are going to Munnar, I would suggest you to not to stay at the centre. Ananchal, chittrapuram are some of the places you can consider.