Grafitti can be tricky, but chemicals are unfortunatly necassary. What kind of grafitti did you remove? Without chemicals is amaZing. The problem we have faced has been a multitude of different paints & different type trailers.
There are Post & Rail trailers which are your standard panels that are a very durable paint that can withstand many different grafitti removers/paint removers.
and the real monsters are Plate vans which have an entirely differeent type of paint that is easily destroyed when using removers.
We charge anywhere from 1.00-5.00 sq ft, based on quantity, logistics, severity & trailer type.
Using chemicals from paint & varnish remover to alcohol. Test areas & have multiple products availible for the discovery process. Don't give a fixed price until you have done a full unit. And consider the sales potential of every client when finalizing costs.