Lots of roller cams come on cast iron cores. Even solid rollers.
They cost more because the core is more expensive to start with. It's more time consuming to grind 8620 bar stock than cast iron. Once the lobe is roughed in, it needs to be heat treated, then finish ground and polished.
Regrinding a roller core can go through the hardness so you can't change the lobe very much, unless you redo the heat treat and then you get into the cost of a new cam.
