What rates would a muralist charge?

Charge per hour for both planning and painting, add the cost of materials then add a premium for how awesome you think you are. If this is your first mural you might have a tough time charging very much depending on who’s commissioning it.

It sounds to me like you’re trying to hire a muralist (not that you are one deciding how much to charge), any clarification on that point would be helpful. If you’re trying to commission a mural without breaking the bank, on idea might be to see if you can hire art students at the nearest university to do work on the weekends. Without knowing the particulars it’s kind of hard to say, but I do know that college artists typically are strapped for cash and would love to work on a project where they can put their artistic skills to good use and make some money too, plus it’ll help them add to their portfolio.

The artist most likely will require a down payment for the concept.
Once he/she starts the art work it will either be or a combination of the two:
Cost of supplies and time, hourly and by the piece (is it a large piece, small piece, does it require painting from a ladder or a scafold?)
Or the artist may just charge you for the piece but if he/she does that then you should tip REALLY, REALLY well.
If you are ALSO hiring an artist to paint an exterior wall that faces the public I highly suggest tipping in the hood of 50% as to keep your wall clean and safe from taggers.
If you are hiring someone from that community and you piss them off then they are most likely to come back and piss you off.
Now, if you hire an artist and he/she sucks (can’t go from paper to mural)
Then you should hire an artist from outside of the city to come fix it. Not someone in the circle.

These are really helpful answers. I’m still not sure is square footage or height from ground would affect the price as well.

Height from ground will affect artist’s costs: renting scaffolding is pricey but it keeps
the artist alive (leaning ladders do not). See if artist is bonded. As if! Given that artist
is not bonded, you yourself must do everything to keep him/her safe.
Artist probably will not be sophisticated about contracts. So you must write up a contract using judochop’s excellent guidelines or ask your state arts commission for a sample contract. Surprise artist by requiring the contract, which will actually be designed to protect him or her.
Do not get a bad artist just because s/he is cheap.
You can get some slick stuff to paint on over the mural and makes it easy to
get graffiti off. Wait till you’ve decided you like the mural before you apply it.
Artist should make the same approximate wage as any other skilled construction worker unless s/he is famous, in which case you will not be able to afford his or her services at all (I base this opinion on your not knowing how much to pay). Again, check with your state arts commission. They’ll have experience with this. Also, they’ll know about muralists around the area. They may let you look at their slide bank. Have a ball.