i think for khyber the total cost of overhauling the engine is not more then Rs: 24000/=
but first get a good mechanic, because i dont think your mechanic is good enough to say at first that Clutch plate and pressure plates are the main probelm rather then pushing u for spark plugs.....
check any expert mechanic and then ask him about the car....
anyway what is the performance of ur khyber on Petrol????? does ur khyber runs with same acceleration and speed on petrol????