It will be easier by flight. However, there is no direct flight from Kathmandu to Nanjing. But conjoint flights with transfers at Guangzhou or Hong Kong are available. And it would be cheaper by transferring at Guangzhou. For tickets booking, you are suggested to contact some booking agencies in Kathmandu as the international airfare would be more preferential at the departure city. About payment, personally it will be safer if you send the money by Cable Transfer or Western Union.