You can choose any of the following options:
Flight: It will take around 1 hour to reach and the cheapest flight costs around Rs1,500. By Bus/Car: This route is quite pleasing. However, it can take around 12 hours to reach. Bus tickets for sleepers/volvo will cost around Rs 1,500. I would suggest taking a bus, since it drops you comfortably with the ease of enjoying a scenic journey with food stoppages. But if time is an issue, better catch a flight. You can take a train from Joginder Nagar too near Kasol, but it is not very convenient since you need to travel around 140km just to reach Joginder Nagar station.