You might be able to get some kind of deal on the Towbar when negotiating the purchase price on a new KL. I can't tell you how much our Towbar cost as it only says "included" in the Options List, with a final (total) figure all up of the vehicle (including options).
If, however, you want the Towbar supplied and fitted after purchase, I remember seeing them, supplied and fitted, for around $950 (Class 4 - Heavy Duty Towbar).
I see on Towbars Australia Home | Towbars Australia
that you can buy the Class 4 Towbar (not fitted) for $633.