Does anyone know how much it costs to find a parent incompetent?

sbopie, your father can be "found" incompetent by his doctor for not much out-of-pocket (his medical insurance will pay some, most or all), but it could be tricky to get his doctor to test him unless you have POA for health care or your dad is cooperative. If you have his financial and health care POA already, or if you have his POA contingent upon him being found incompetent by one or more doctors, then that's probably all you'll need to protect him.

But if you don't have his financial and health care POA and want him to be found legally incompetent by a guardianship and/or conservatorship court, that will cost a lot more -- the $10k-$12k previously cited is a good estimate, but could be even higher if any relatives contest. (It could also be a lot less if you find the right attorney to assist you and no one contests.) The court will require that your father be evaluated by a doctor, so getting his doctor's evaluation before filing for guardianship won't be a wasted step. If your father's income and assets (other than his house) are minimal, then you may be able to get nearly free legal assistance from Legal Aid in your state and/or through the guardianship court.  Good luck.

FWIW - I was told by an attorney that it would cost $10-$12,000 and could take 3-6 months for my father to be declared incompetent. There are legal fees and court costs involved, and a temporary guardian may have to be named. That person is often a retired attorney, and charges a fee as well.