Hi Giovanni,
Unfortunately it is not possible to access the change history via the
API. You are also correct that it is not possible via the
ReportService to obtain the Max CPC on a given day. I think your two
best options would be to either:
a) Make an API call each day and record the Max CPC. You can use
these values later for analysis.
b) Use the ReportService to determine the Average CPC on a given day.
This won't match the Max CPC exactly, but it should correlate.
Best,
- Eric Koleda, AdWords API Team