What is fair compensation for handling administrative and financial matters for an elder with Alzheimer's?

My mother recently passed. I always handled all of her affairs as well as my step-dad, since she started declining, about 10+ years ago. They always offered to compensate and I always declined.  Now that Mom has passed, my step-Dad, whom I love dearly, is again insisting to give me something for my efforts. Dad lives in assisted living. I handle all of his finances. He still owns a home and I pay the property taxes, the utilities (my step-brother lives there for free and is indigent), and any maintenance required.  I handle all of his medical payments and I drive him to appointments since he is unable to drive.   I lunch or have dinner with him regularly, at least 2-3 times per week and call him daily.  I am his primary contact for everything and I have held his POA and POAH for years now.  I am the executor of his estate once he passes. He saves his mail for me and we go through it regularly and I handle anything that comes up. I co-own his bank accounts and credit card and pay anything that needs paying.  Dad is a proud man and wants to pay me something and now that Mom has passed I am willing to accept but I want to be fair and don't want to be accused of taking advantage. His 2 sons are both unwilling and unable to help him - they are his the sole beneficiaries of his estate.  I am not poor but any small amount would be helpful. What is a reasonable amount for the administrative services I provide that we both could feel good about and would not raise any eyebrows?