Hi Dan! Good to see you here.
Okay, so there are basically four variations you can build:
A. 13515-13574 with diagonal panel roof and original windows
B. 13515-13574 with diagonal panel roof and blanked windows
C. 13575-13664 with X panel roof and original windows
D. 13575-13664 with X panel roof and blanked windows
Version A: $107.27
Version B: $107.69
Version C: $105.10
Version 
$105.56
Then there are the detail parts you can add. Because of the $5 setup fee per part for parts printed in Frosted Ultra Detail (FUD) and Frosted Extreme Detail (FXD), I tried to group parts together on a sprue to avoid paying $5.75 per small part. This way I get multiples of small parts and only encounter the setup fee once. The prices vary between the two materials, with Frosted Extreme Detail being the more expensive and more detailed material. It also has a smaller maximum size, so some things like the caboose sides won’t fit in the bounding box, therefore I can’t offer those parts in FXD.
The detail parts that apply are as follows:
E: MP Smokejack $9.72 FUD/$12.95 FXD for 10 pieces
F: MP Battery Box $11.54 FUD/$16.07 FXD for 2 each of 3 styles (total 6 pieces)
G: Brake Rigging $10.60 FUD/$13.46 FXD for 4 pieces
H: Toilet Vent $9.08 FUD/$11.85 FXD for 10 pieces
The prices are still higher than I’d like, but when I think about building another one of these, or in the case of the 13575-13664 series, which I have no possibility of obtaining other than brass, it’s not that bad. You still have to provide the Atlas caboose to supply the trucks and underframe, but you can get those pretty cheap on ebay regularly, especially if you don’t mind stripping one in the Cotton Belt scheme (those things are everywhere!).
I hope this answers your questions. Of course, if you have any other questions, feel free to ask.
Ryan Harris
Fort Worth, TX
