There really is no "price per acre" because there are many deciding factors for what will determine the cost to bring a site to "pad ready" which in itself does not give enough information. For example, there are at least 3 possibilities for bringing water to the site. A well, tapping in to a water main at the site property line, and having to install a water main extension to the site. As you can imagine, the costs increase exponentially as you escalate through these options.
As far as earthwork goes:
These numbers are a few years old, but these were good prices at the time:
Strip and pile topsoil : $1.50/cu. yd.
Move cut/Fill : $1.00/cu. yd.
place/compact fill : $1.00/ cu. yd.
clearing trees : $1k/acre
grubbing: $1.5k/acre
These numbers don't do you much good unless you have some idea for existing and final contours or elevations
I would maybe add to your final number based on these estimates an increase of 10% due to inflation, fuel prices, etc.
A rule of thumb for commercial work is $3000-$3500 per parking space.
Of course, these numbers don't include sewer, water, erosion and sediment control measures, road work, power, permits, etc.
Depending on what part of the country you are in and the existing topography, site work can be one of the largest sources of project over runs.