Pricing artwork is notoriously difficult; but, basically, you get what you pay for; however here are a few examples.
Portraits:
An oil portrait about 45cm. x 65cm of one person with a fairly simple
background would start at £650. Add about £200 for each extra
person. If you wanted someone in a Queen Elizabeth dress with all the
jewels, start at £5000!!!
Murals:
These vary even more due to some people wanting lots of sky, and some
people wanting a street market. However a reasonable amount of detail
on a simple background could be from £120 a square metre. A very
detailed window with lots of plants and ornaments in the foreground could
be £300 a square metre.
To remove the pressure from the pricing situation, I offer a free visit
with estimate within a 30 mile radius of my home (Ealing, London).
Beyond this I would charge 50p per mile. If I come to see you and you
don't want to order anything, that's fine.
If you want me to produce a sketch in watercolours, and then not order,
I charge about £30 an hour to produce this; you don't pay this
if you place an order. A usual amount is £70 - £100.
Any other drawings, paintings or sculptures need to be estimated on that first visit.