Costs to Run A Ranchworx Roller Chopper

I am developing a cost estimate for a large ranch and trying to compare hiring contractors to do the work of clearing about 2,300 acres of land covered up in varying amounts of mccartney rose, chinese tallow, prairie willow, etc. I have it broken down into NRCS rates of brush cover. Located around Gulf Coast of Texas. Ranch would probably be open to contractors if the price was somewhat comparable to purchasing the equipment. They have a 180 HP tractor, but would need to have a solid undercarriage installed and foam tires no doubt. They are most interested in the Ranchworx triple drum pasture renovator. They will then follow up chopping with a ground rig and some Grazon P + D. Any information would be helpful, especially a formula for calculating costs per acre including depreciation, purchase price, etc. Thanks!