It seems more like 188 000 in cost for the first ones is unbelievably low.
I did statistics on my commonality for the 737-400 when I was running a single type.
The cost per a/c only gets lower by each plane even if its by a very small margin.
I started my calculations at 27 737-4 which gave me a cost per plane of close to 55 000 in commonality cost.
Number - commonality cost in thousand per plane
27 - 55
50 - 51
98 - 49
127 - 48,50
Arriving at 127 of 737s obviously took me a while and the normal inflation that exists in the game are not weighted out. I wish we had some kind of inflation index to follow!
My numbers doesnt show any trace of what Sigma calls "big jump in costs" or the OPster says and show that the cost is decreasing quite steadily even if its in a very small pace especially after 100 planes.