I dare say most of them are made by U.S. Radiator.
http://www.usradiator.com/coresI recently purchased a radiator from Dillion Radiator for $200, for my 50 Coupe, shipped to my front door. I have no problems with the one I got. Appears well made and I've ran it a few times. I think you can get one for the same price....they don't make them but have good prices. Mine also came with a nice good radiator cap. BUT it is aluminum and you may want to stay original, which will cost you as you already know.
http://dillonradiator.com/Take your time and do the home work.
Back when I bought the Desert Cooler original type copper radiator for my panel it came from JimCarter and I got a confession that it was. I also got my tranny cooler in it and the cost 3-4 years ago was just under 300 bucks but that was before copper went out of site.
Good luck.