I can suggest one if its idukki and munnar it's a mahindra jeep and good for off road only he also has a force gurkha type vehicle rest of kerala I don't know whether he will take up but I can share you his number contact in 7736834619 he was my guide and those offroad rides and that trip was awesome
There is a guy usually i arrange bookings for my North Indian and South Indian friends when they visit Kerala. He is having an Innova Crysta and an Ertiga and he can also arrange other vehicle on request. So far all my friends are very much happy with the price they paid for as well as the service. His name is Biju and contact number is +919846178902
I had hired a car for 4 people in 2016 from a company called Pepper Kerala for 5 days. Pickup point was Ernakulam railway station and drop point was Cochin. You can check them out. Email id: pepperkeralaholidays@gmail.com