Hi Guys,
I actually think that this is the standard coupler and Marklin sells them in packs of 50 for about EUR8.00 (ie 0.16 each)
The current conducting ones are about EUR8.00 each.
So if you want it as a current conductor then yes they are expensive.
As for Roco and Fleischmann, personally I would not use the Roco ones (IMHO they look horrible when uncoupled). Personally I use Marklin heads on my freight stock and Fleischmann on my passenger stock.
Cheers
John