How accurate is your top dresser? My plan was to do about 1/4" applications once a year for my customers. At a 1/4" depth application a yard should cover 1296 sq ft but to play it safe I would budget for it to cover only 1000. With mulch the math shows a 2 cu bag will cover 19.2 sq ft (at 1.25") but in reality it never goes that far. We probably average closer to 12 sq ft per bag. I'm trying to be safe and factor in there will be a fudge factor with top dressing as well. It's not like the top dresser is some scientific application machine with extreme accuracy. With fertilizer applications something as simple as high humidity can vastly effect how material is spread. It's going to be a given that the varying moisture content of the material being spread is going to effect the accuracy of the true application depth. What prices are you able to charge for a typical application where the material being spread is going to cost you about $30 per 1K of coverage? I'm thinking you've got to be able to charge $35-$45 per 1K coverage for labor to make it worthwhile.