With fuel and machinery prices what they are plus the wages for the operators and truck drivers (Davis Bacon rates)....
Davis-Bacon wages only apply to public works / federally funded projects. Excavating a hill on private property doesn't require payment of Davis-Bacon wages. The road project you cited does as part of the funding, no doubt, included a federal grant of some kind.
The closest you can get to an accurate estimate is to call several local excavating companies and ask for an estimate. If you have access to RS Means, you can probably estimate the cost within about 5% if you put in all of the adders like equipment, transportation, part time supervisor, and do the appropriate city cost index adjustment.
We generally develop a "crew" for this type of project as you will have to include some supervision time. For a small job like this we would probably add 1/4-time supervisor (have to include travel time, not just time on the site).