Its illegal to touch mailboxes.
Second thing is that is way too cheap. with a 4gpm machine up to 1k sqft that a minimum of 1hr worth or work (realistically longer). So if we were to break that $50 down to how much you will be making, your not making anything and could probably make more with a stable minimum wage job. Not trying to be offensive, but if you are starting a real business then you should be aiming for much higher.
Also just a tip, because when i started all i really wanted to do was driveways, less risk. Driveways dont make any money, House washing does then up sell the driveway, pool, ect. It would take 8+ $50 dollar driveways to make what my average is on a house. You will be driving all over town for $50 bucks when you could just do one house. My .02 is that volume is not the best way to build this business, i know guys who like to brag they are weeks booked out, but when you know they are doing 2-3 house to the price of my 1. Who's really making more money? Pricing can be very complicated, im still working on my mine.
Also curious if you have a business name? The caricature of your head im assuming is a logo, but whats your name? I didnt see one on the business card or flyer.