The answer, according to Bronco6G, is $5,000. For the money, you get black-painted 17" beadlock-capable wheels, 35" mud-terrain tires, electronic-locking axles, a high-clearance suspension, 4.7:1 final drive, and position-sensitive Bilstein dampers. It's the quickest way to go from off-road-capable to trail-conquering legend, although it isn't available on every trim, and most notably, Ford says, it's "currently not available with [a] manual transmission" - something that's irked some purists.
The survey sent to Bronco reservation holders also appears to include pricing for myriad other options. We now know, for example, that on models where the 2.3L EcoBoost four-cylinder and seven-speed manual come standard, stepping up to Ford's 10-speed automatic transmission will cost a not-insignificant $1,600. On those models, the 2.7L engine with ten-speed auto is a $3,500 upgrade, or a $1,600 option on the Outer Banks model, where a 2.3L/ten-speed combo is standard.