I can't find anything on it either but you could come up with something fairly easy. It just depends on a few factors:
1) Size of the mansion
2) Size and quality of the Staff
3) Size and quality of the guards
4) Area in which the mansion is located
Thus far nothing official but you could go off of what people normally earn (for instance a commoner earns 3gp/month).
Also, the PCs would have a hand in this as well. There may be a certain "price" demanded by certain staff members, and depending upon the quality of the staff the cost for maintaining the staff could go up but the cost of maintaining the building itself could go down.
Additionally, the size of the mansion will, obviously, be directly proportional to the size of the staff/guards.
Lastly, if the mansion is built in a very rich district then the staff hired would expect a certain level of pay while if it was in a poor district the staff would also expect differently. Of course, the poorer the district the more likely the PCs are to get robbed.
