I would consider making you're own as they are nothing more than 3' long steel tubes with two holes drilled into them. Cost is approximately $75 each. Each screw is about $1.75 each, so you have another $7.00 in JD hardware. (These are internet prices)
For under $15 in supplies one could make these with common hand tools. With the money saved you could have them gold plated and still be under dealer pricing.
John Deere Tube M164773 (2)
John Deere M162365 Screw (4)
2012 JD855D OPS Black Poly Roof, Deluxe Cargo Box, Front and Rear Protection, Power Lift, Front Hood Rack, Rear Screen (homemade), 800 Watt Inverter, 2500lb Winch installed in cargo bed, Front and Rear LED auxiliary lighting (4" square 27 watt), Front and Rear CV Guards, Koplin Side Mirrors