Do you have any idea how much 400 to 600 yards of dirt is? Assuming the standard size dump truck bucket hold 6 yards ought to give you an idea it will be around 100 truck loads.

To raise the grade 1-inch per 1000 square feet takes 3.2 cubic yards of material. Depending on where you live a single truck load (6 cubic yards) of mediocre top soil will cost anywhere from $75 to $250

Welcome to the forums and thanks for not really doing anything before asking for suggestions. Too many people would have waited until they dumped a few truck loads of junk and then asked for advice. Is there a house on the property now? That much soil is guaranteed to change your drainage to something much different from what it is now. Are you sure you want to do this?

Can you post a picture so we can see what you're dealing with? Usually there's nothing wrong with a slope. Maybe someone will have a different way of looking at your issue that you have not thought about.

For new construction they first build a pad for the building, build the building, then call in a "finish grader" to prepare the soil and profile it according to the landscape architect's drawings. The finish grader will use a tractor with a box blade attached to the back. A really good finish grader can prepare 5 acres (flat) in a morning if there are no trees, sprinklers, or concrete in the way. If you want it profiled it might take the rest of the day to do 5 acres. An average driver might take twice that long to do the job, but that's about the limit of the job.