How much to charge for drawings?

Hiya, hope i'm posting in the right place,

I share my work on instagram and someone asked me how much I would charge for a drawing of them? I have no idea, to be honest I wasn't expecting anyone to ask me so I never thought about it. This is my instagram if you want to see the quality of my work: instagram.com/mssallyshep
It would probably be the quality of the blue drawing of Masie Williams.
But yeah, any suggestions?? I don't want to undervalue myself but at the same time fdon't want to overcharge anyone!

Thanks in advance <3

When a price is not fixed, a deal is made between a seller and the buyer, therefore, you will have to compromise with each customer or make a fix price.

If the work took long enough (like 10 hours+), then do charge high (+50£), if it takes two hours or less, then it would be good to charge low (<10£).

I would say:
Thank you for showing interest in my drawings, I am not sure about the price, could you please give me an offer and your picture? So I'd know how much time it will take to make and how much you are willing to pay. After that I can make a decision Thank you!

Please be aware of copyright issues, once you sell, it is not your drawing, but theirs. You won't own it, but you can be regarded as the author/artist.

If the request is from a kid, you can charge 5£ or free xD ... Just my opinion...