Gino..I agree on the advertisement design layout is not worth the money.
But also it was a quick effort ..So this can be improved & made to be well worth the money & more.
One way to find out what they are willing to pay is ASK what there budget is for advertisement at storefront sure they will say much lower.. but a start.
Now it is up to you to prove that this is worth alot more.
Explain the process of cleaning, designing software & equipment, materials used & cost of each, plus your time involved, start adding it up, ask them about there charges for whatever.
Now they will start seeing the bargain they really are getting by seeing the cost to produce.
Also explain how low cost storefront advertising is by..PER DAY basis or even weekly or monthly ..they will begin to realize the SIGNS ARE the cheapest advertisement on the market , when comparing to TV ..Newspaper, Magazines, , Internet so on & so on & do not let them say well it is on my property another excuse.
Also your ability does not come overnight & anybody can do this & stay in business
There is alot more ..but read some sales books like how to close a sale