Purchase price is only one part of equipment cost. Financing, depreciation, fuel, labour, maintenance, wear components, insurance and mobilization belong in the same model.
Ownership costs
Include financing, insurance, storage and expected value loss over the holding period.
Operating costs
Model fuel, planned maintenance, repairs and wear items per annual operating hour.
Mobilization
Allocate transport and setup across the work the machine is expected to complete.
Stress-test assumptions
Use low, expected and high cases rather than one confident-looking number.