Your best bet if you are thinking about getting into top-spreading would be to skip the bags and get either a truck bed, trailer, or dump trailer full of organic compost.
I did a quick Google search in your area, and here's a link for bulk organic compost at $25.00 a ton (just a quick scan of their website).
Their address is: Silver Creek Road NE in Rochester, MN
This would be your best bang for the buck. Plus shoveling higher than your top dresser machine is easier when your above it. Just pick up a little step stool to step in and out easier.
I can move about 10,000 pounds of compost in 4 to 5 hours. And you should charge about $60 to $100 a ton. This would include organic compost, delivery, spreading, clean up, and the customer buys their seed.
So if the seed doesn't germinate....then it's their problem and not yours. I just direct them to the "Big Box Stores" since they usually have a high turn over rate of material....because with all this work you put into the yard....if the seed is not good....then the customer isn't getting all the benefits of organic compost.
2,000 pounds (1 ton) of compost for $25.00 or 2,000 pounds (1 ton) of bag compost (40 pounds a bag @ $4.00 or higher per bag & tax) would = $200.00 or higher at Big Box Stores.
Go with the local compost and get something to haul it.