Ouch $18 per flat? I am at about $13 per flat cost including soil amendments and fertilizer with 4" cup size.
I try to get $40 per flat if more than 10 flats, and $50-60 if less than 10 flats. I think there is a better way to do it... like charging per sq ft.
So far we have put out 600 flats with a few hundred more to go.