Range is from Rs 500 to Rs 700 one way. Try to bargain to 500, if nothing works out then 600, last resort 700. Thats normal fare, and 550 is how much I paid 10 days ago. When you get off the plane, just make sure you dont travel via birtamode, thats long way, talk to airport staff, you can even get a tempo that would take you half way upto dhulabari or somewhere, and from there to kakkarvhitta from another means. But hiring a taxi will be peace of mind. It will take around 15/20 mins approximately. You can get taxi for 2000/2500 upto Dharan from Kakkarvhitta so Jangali manab it doesnt cost that high price from bhadrapur to kakkarvhitta.