look for a normal 2/3 ac fare in a superfast non rajdhani train. the difference in fare is the amount for catering etc. similarly for shatabdi express - look for ac chair car and find out the difference. other costs are the same. for e-g for travelling delhi-mumbai try fare in Paschim Exp, or Golden Temple & compare with Rajdhani. Similarly delhi-dehradun (or some other destination) look for ac chair car (delhi kanpur) like janshatabdi/gomti and compare with shatabdi. trust this clarifies the position.