The construction of any object has costs that are associated with it.  Not all of these costs are measured with money! Things such as the loss of a forested area where people used to hike for relaxation due to the bridge's construction will have a very large negative impact on people's lives, and should be taken into account.

Log Entry #7

What information exists about the bridge you are researching in terms of the construction costs? Most large projects that have been built in democracies are very expensive and are often funded by governments, who must report their spending to the citizens they represent.  This means that the costs of the bridge are often available.

Of course you should try to look beyond just money to determine costs as described in the first paragraph above.

Record the results of your research in this area under key question #7 in your research log.