Then there is the cost of the dies.
https://www.midwayusa.com/product/46...ding-2-die-set
The 357 Max is indeed an excellent chambering; I have two. My favorite Contender barrel is the one made for me by Bullberry, and marked 35RemR. It is a 35 Remington with the addition of a cut for the rim of the 303 British cartridge.
Making the cases is a bit laborious, but no more so than for the 30 or 35 Herrett cartridges. They seem to last forever, which makes my supply of extra 303 British cases redundant.