How much to pay hairdresser?

[MarciaMarciaMarcia]

I have been living overseas for the past few years, so have no idea about prices in England. My sil is a trainer hairdresser but currently does it one day a week out out her home, while she focuses on her other business. I know she pays taxes on her hairdressing.
I want a cut and color. She says there is no charge, but I want to pay her. Is £40 reasonable ? Or am I way off base? She is in the SE if that makes a difference. What should I pay ? Thanks

Do you mean highlights or a tint. Cut and highlights I paid £70 recently and that was cheap.

No highlights, just covering the grey!

I pay 70 for head of 1 color and cut. At a salon.

£40 would be reasonable just for a cut and blow dry . I would say £80 for a colour, cut and blow dry

But if she was offering for free then £40 is plenty