How much does it cost to be a financial guardian?

In addition to legal fees, the court in your jurisdiction may also require the Guardian to obtain Bond on the value of the Ward's estate, if it's for Guardian over their assets. The Bonding company usually charges a fee for this. You can call around and get estimates. For Guardians over healthcare matters, they don't usually require bonding for that.

That depends on whether anyone will fight you, including him. Uncontested Guardianship can be done in one hearing for about $3000. See an attorney to start the petition for court.