Christine,
you might check the Employment Wanted or Position Wanted sections of your local papers to see if you can find an independent with suitable references and qualifications. You might look in elderly care, as the confusion and other issues you are dealing with are similar. An independent would likely get you a lower rate, but you would need to consider insurance and other issues that an agency would take care of.
Your county social services department might have programs or at least ideas.
A minister or rabbi might be useful. Maybe the local American Cancer society?
Thoughts are with you.
Maria