How do I find what a reasonable rate of pay is for time spent dealing with mother's finances?

Be very careful, as those below say. You have agreed to take over as POA but there is not inplace an agreement by contract for pay. I am doing Trustee of Trust and POA for my brother. Both of these things take a lot of time, especially in this first year when everyone wants all the information mailed to them, and get all the address info confused and etc. It is not an easy job. I do not take any money for this and in fact am meticulous in proof by check copies, and etc that every cent paid out is paid out for him.
Now at the same time his friend has a POA, a court appointed fiduciary. That man charges 90.00 an hour. He is good at his job, so his hours are minimal, and things I worry over and spend time on he would likely not even address at all, because he knows his job.
If you do not wish to have this job it may be time for you and your Mom to get a paid fiduciary. They are licensed (tho the getting of a license doesn't cost a whole lot or take a whole lot of time, just skill, and they are accountable to the courts.)
Good luck.

Be careful. If your POA does not specifically allow for you to be paid and your parent has Alzheimer’s and is not competent to agree to a contract, it can be viewed as you unduly enriching yourself if Medicaid comes into the picture. If you are able to set up a contract, Money she pays you will need to be declared as income and you will need to pay taxes on it. There is a 5 year lookback from date of application on money spent when you apply for Medicaid to help with long term custodial care in nursing home. Medicare does not pay for long term care in nursing home. Many families are unaware of the lookback and the consequences can be devastating. The view of many states is that family should assist as support of their loved ones, especially if the help is sorting out finances.

Does your POA agreement state a rate of pay? I know the one I have for Mum, does state a rate of Pay. The POA has not been sprung yet, but the pay rate is tied to minimum wage. Off the top of my head I think it is $10/hr over minimum wage.

If your agreement does not include this information, I think your best bet is to get quotes from various bookkeepers on their hourly wage and use an average of those rates. Make sure you keep detailed records incase you have to deal with a Medicaid look back,