cheapest manufacturing process for low volume horn antenna production?

Hello again! I am searching for cheapest manufacturing process for horn antennas. Quantities about 100pieces. I ordered cutted thin copper plate and standard flange waveguide. I thought it will be pretty easy to make conical hor by soldering flanges of copper sheet, because all sizes was calculated and looks nice in CAD. But in reality i did not get good result, as copper sheet is too difficult to put in conical shape. Using thinner copper sheet gives too poor mechanical stability and horn is easy deformed. Can't use pyramidal horn and commercial horns as they do not perfectly fit to cylindrical enclosure my client want to use. Currently i think about buying commercial horn of smaller size and glueing some material on the top to perfectly fit enclosure. Any ideas welcome, thanks!

What are the dimensions? Have you tried to reinforce the outside of the corners with pre-bent brass angle?
Frank

I recently heard of a group having success with electroplating designs constructed with conductive ABS plastic on a 3D printer. I'm dying to try it and see if it finally makes it possible to prototype corrugated horns!