I've never heard anyone mention the BX6730 factory cab for the BX2230 (nope - I called - it doesn't work with BX23). But this puppy looks deluxe - with 33,000BTU heat built into the ceiling, wipers, lights, HD alternator - the works for list price around $4k. Here's the factory page.
http://www.kubota.com/h/Products/bx1830-2230.cfm
http://www.kubota.com/h/Products/bx1830-2230.cfm