Yes, if you add features to the project after we have agreed on the proposal, the cost will go up. A recent project included a portfolio section, which I was assured would be “about the same size as the current site.” Current site = 10 portfolio pages, with 26 photos. By the time we were done with the new site, it was 15 portfolio pages with 70 photos. And yes, the new photos were sent to me for cropping and re-sizing. In the end, the project went over the estimate by a few hours, due to this and other feature enhancements.
And still the client seemed surprised at the additional cost. Really?