Is a Home or Building Contractor Bound by a Written Estimate of a Job?
As a general rule, a contractor is not bound by an estimate, written or otherwise. Unless it states it is a binding contract, it is not enforceable.
What an Estimate Covers
For example, in a kitchen remodeling, does the estimate cover the cost of such expensive items as new appliances, cabinets, and countertops? Some estimates include only the contractor's labor. Others include both labor and materials; and some may cover the cost of the total project, including the subcontractor's labor and all materials. If the contractor offers to get the materials, ask if there is an additional charge for the time spent in obtaining them. Also ask if you will be charged the retail price or the discounted "wholesale" or "contractor" price on supplies. It is also a good idea to check references and ask former customers if the estimates the contractor gave before the job matched with the final bill.
Home improvement projects often encounter unanticipated circumstances such as dry rot, which can significantly add to the cost. However, client changes are often the culprit for cost overruns. If the contractor suggests a change, always ask the cost implications.
If you don't think there is a good explanation for the difference between your estimate and the final bill, you may seek recourse through a local contractor's guild or the Better Business Bureau. If that doesn't work or you suspect fraud, contact an attorney. Merely not paying the bill can cause future problems if the contractor files a "mechanic's lien", a legal claim attached to your property. This can make resale difficult.