I do not understand what you mean asking what is the going rate, I believe it costs £110 to register a Lasting POA for financial matters, there is also a Health POA which is quite separate and would need to be registered.
You, as donor, can give a Lasting Power of Attorney to your Mother or she can to you providing the donor has mental capacity. There is a Helpline 0300 456 0300
Sorry, perhaps I did not explain myself very well. My mother who is 90 wants to give me POA just in case anything happens to her. I have looked into doing it on the net, but it looks very complicated. I just wondered what solicitors charged and if there was a standard fee.
The cost will depend on the individual solicitor you choose,ask around in your area.
As a rough guide I obtained POA via a solicitor in 2012 for my mother and it cost me £480 in total. I felt it was money well spent as they filled in all the forms and visited my mother to confirm that she understood why it was being done.
A country Solicitor will probably charge around £150 to £250 per hour plus Vat together with any disbursements. The forms are quite long and in 3 parts they will be rejected by the Office of the Public Guardian if there are any errors which will add to your registration fee.