Nice work!
Just out of curiosity what was or is the customers budget? What were/are his expectations for the car?
From my experience customers have "scope" creep, which means they continually think about new or different things to do. The problem with that is what you are facing right now he doesn't understand what those changes mean in time and money. Communication is key and it sounds like you both aren't on the same page. Remember it's "his" car so getting on the same page, with the same goal is paramount. Building a car is all about comprimises if he wants it done for a show, then a path needs to be laid out for him to get to that goal. He will realize once shown what the car will look like going down that path. And he may be alright with that...