Unit costs are a great analytical tool.
Take your machine O&O costs per hour, apply that to how many hours it takes to move X amount of dirt, lay X amount of stone or gravel, what have you.
Then add whatever your costs are for materials in unit costs as well–yards of dirt/gravel, square feet of pavers, sod and so on.
Then you have a unit cost which not only greatly simplifies bidding.
But you can also use this as a tool to analyze performance of crews, machines and even subcontractors.