Well, depending on how you want to do it, there might be a way. I noticed that there are a couple of lines in the ElementalDefs.xml that look like this:
<!-- ** City Administration ** -->
<CityAdminCostExponent>0.0</CityAdminCostExponent>
<CityAdminBaseCost>1.0</CityAdminBaseCost>
You could mess with these values after copying and pasting the file to the mod directory. I assume that the cost would be in gold, but I can't confirm that the values do anything, atm.
Anyway, if you go this route, and the tags are, in fact, hooked up, let us know what values seem to work well for you. Happy modding!