I think you are asking how to get electricity into an existing wall to add a wall mounted light.
If it is an interior wall with attic space above, I think the easiest way would be to drop the line down into the wall from the attic. That is provided you know about wiring from one ceiling fixture to another and to a switch. You should probably get an electrician or at least get help from someone who has done this before.
This is not a beginners’ project and you need an electrician or at least a certified/licensed Handyman.
You can get apples to apples bids by defining the Scope Of Work. As in what exactly do you need? Where is the electrical feed coming from? What kind of load are you going to have, as in how many watts (how many light bulbs)
You need an electrician or someone who has worked with electricity. Either a separate line through an attic or basement. If there is an existing outlet on the wall wiring can be fed from it to where you want it.
I'm a handyman with a lot of years do so. This IS NOT a
job for the average Joe.
I totally agree with " William and Lifestyles Home "
Be safe and get a PRO...