Going out on a limb here, but to power wash the wall will be one day with 2 days to thoroughly dry, in your area. Might be a total of 2 hours, according to drive time.
Prep the wall, draw in the circle with a primer and then a top coat will be another 2 hours, but you should be able to start cutting your letters in almost right away. Start at 6:30 and be ready to letter by 9am. Not knowing the copy, but you said it was simple.... maybe 2 or 3 hours tops. Have this in another thread where I did 18" letters across the top of a building in a bucket truck and it took about 1.5 hours to do each wall..... one on either side of the hangar. If you're on scaffolding, it might take a little longer for moving things around.
Probably around $1,100 or so.
Next time, put this in the correct category, so we can discuss it normally.