OK this may be a silly question, but does that JD have a 3pt hitch? And what method is used to power the tiller?
I suspect, that is a proprietary tiller that does not used a standard 3pt hitch and is not powered by a standard PTO shaft.
I have a 10 year old Cub Cadet front mount snowblower, it cost me almost $3000, but that is the ONLY blower that will fit my tractor. I also have a much larger Farm King blower for the 3pt hitch of my larger tractors and it cost me $1400 this past December. What I am trying to point out is that the manufacturers hook you on a tractor and then upcharge the heck out of their proprietary equipment because that is the ONLY stuff that fits the tractor.
You may find a pull behind gas powered tiller for about half the price in the Norther Tool catalog or at TSC that are made for small garden tractors.