It wasn't clear in my first comment, but it is representative of a company, not an individual. We're fortunate to have a great team estimating and scoping projects and great developers on staff staying on budget; it's rare that our actual rate is less than what I've cited, and we don't cut scope to stay on budget. Estimating, by far, is the hardest part.

If the app isn't to our internal standards, we'll do whatever it takes to get there, even if it pushes us over budget (ie, staying up until 4am).