Jon, A close up of my cars, made from a Don Winters’ kit:
(http://jbrr.com/Pics/RollingStock/LogSkeletons/IMG_5234.JPG)
These were cast parts, but if I were doing it on the cheap, I’d sure be looking at some styrene I-beam from Plastruct. I’d cut some thick styrene strips at an angle for the end parts. Head over to Michael’s and get some rings to hold the chain - or bend your own from brass rod. A few bucks and you’d be able to do your whole fleet.