The Rule that addresses this is:
2. For filing a petition for guardianship of the estate under ch. 54 or an application for conservatorship under s. 54.76, if the value of the property, less encumbrances, liens or charges, is the amount specified under s. 867.03 (1g) (intro.) or less, a fee of $20 and, if more than the amount specified under s. 867.03 (1g) (intro.), a fee of 0.2 percent of the value of the property, less encumbrances, liens or charges.
3. The fee shall be paid at the time of filing of the inventory or other documents setting forth the value of the estate in the proceedings.
That is Rule 814.66 accessible here: https://docs.legis.wisconsin.gov/statutes/statutes/814/II/65
It is the ward's assets that are to be used to satisfy the fee:
Use form GN-3440.
- File the inventory within 60 days of your appointment as guardian; and
- Pay the filing fee. The fee is paid from the ward’s assets.
- For estates of $50,000 or less, the fee is $20.
- For estates of more than $50,000, the fee is .2% of the net value of the property. Your inventory cannot be accepted unless you also pay the fee at the time the inventory if filed.
The ward's separate property assets would be used first to satisfy the fees:
If the ward has insufficient separate property, then marital property would be used as spouses have a legal duty to support one another.
Here is a guide that details the duties/responsiblities of a guardian: