I was quoted £475 (i.e. standard retail) + £250 for a single MTO with a 6-8 week turnaround. That was for a version with a full bellows tongue, although to be honest I was expecting a price increase for that. Presumably a GMTO will take longer, but I don't know. From what I understand the zug leather won't attract any additional costs.
I can give you a better answer once we've seen the leather and finalised the spec.