Im about 8$ per tracks. I dont use percentage in this situation, youll end up over charging, and they will certainly say no. The other day, i did 325$ windows with only $60 add on in track cleaning which was like 20 mins of work extra…
I use the track brush, love it. Get a crevice tool attachment with stiff bristle. You’ll get it done faster. 3min avg completion? Not to shabby.