Today, it seems most projects worth having are government funded. As the Feds keep trying to kick start the economy, they continue to pour billions of dollars into public works projects. What makes public works unique to private work is that these projects usually require the use of prevailing wages. Prevailing wage is determined as the average wage used in a specific region for a particular trade. The government usually relies on the local union wage to establish the prevailing wage. The union wage is negotiated by labor representatives and management, so the government has determined this is a fair determination of what the work to be performed is truly worth.
Since most public works projects require every contractor who bids on a project to use a pre-determined established wage for specific trades, and they are bidding on a set of plans and specifications that list what materials must be used, you would assume the bids would be very close to each other. Surprisingly, the numbers can be vastly different.