The price you quote is for the complete job. There are no line items showing a labor rate that seems to be a brain surgeon's rate. There are no line items showing materials that your customer thinks he saw at a home center for half your price. The volatile price issue is reduced to a single number that the customer accepts before work begins. Your business will be viewed more like a high level profession.
Many contractors reduce the amount they charge per hour to avoid confrontation about labor rates.
This reduces their profits because their expenses remain the same. They end up paying themselves little and having spouses who work the books for no pay. Go where the Money is. Utility companies and home centers, like Home Depot and Sears, are selling very successfully using Flat Rate. This is where the money is today.