u r somewhat right............but to add..........one can board a sharing taxi......mostly Sumo............(nowdays Tata Winger too) from Jammu............although Udhampur is nearest Railhead for Srinagar but you will get these taxis from Jammu only.............fare for same will be around Rs 500-600 depending upon your negotiation skills and load of passengers............this total distance from Jammu- Srinagar will take around 5-5:30 Hrs..............
Moreover nowdays due to Amarnath Yatra...........this journey will be completed in 7-8 hrs due to heavy Traffic..........diversions and en-route checking..........