If you solicit bids from several different remodelers, be sure they are quoting on the same scope and quality of work. Discuss variations in price and beware of any bid that is substantially lower than the others.
Don't automatically choose the remodeler who gives the lowest estimate. The remodeler may not have understood the project, may have underestimated what it will take to complete the work, or is simply trying to get a price advantage over the competitors.
Reputable contractors will give you a “fixed price” and stand by it. Fixed price contracts are best to stay within the agreed upon scope and budget.
Most homeowners add items onto jobs as their remodeling projects progress. A reserve equal to 10 to 20 percent of what you expect to spend is good amount for unforeseen additions you may want to include once the project begins.