engine rebuild help

I am about to restore my first car!! My Grandma's 74 dart swinger. Best estimate from you all will help a great deal. It has a 318 and according to my father (where the car is) 500 miles away, the engine is going to need rebuilt. About how much is a full blown rebuild going to cost? I want to do this right the first time and don't want someone talking me into more or not enough. thanks