Sure they can make plinkers... if you love recoil. I personally have never hunted with my CZ550 in .458... I mean, I have been out hiking with it, where if the chance presented itself, I would have taken an animal... but I have not been on a hunt since I've had it that it has been my weapon of choice.
It is still pretty expensive to plink with. But after the initial expense.. you can do pretty well. Once fired brass for the lott costs about 40 cents a case on the bottom end of the spectrum. Brand spankin new stuff usually runs a dollar. Powder is expensive... because you can use between 60 and 90 grains of powder depending on the load. So your powder measure drops quick. The most I have loaded up in the lott was 30 cartridges at once.... and it was devastating to watch that thing go through powder. As of lately, I have started using lead through mine to save some bucks. Still end up being 40 or 50 cents a bullet when you are talking 400 grains of lead, and I only shoot GC bullets in the lott. I also shoot the 350grn hornady sp, which is a little less than 50 cents a piece.
So if you say that brass is already taken care of.... You are still gonna be spending 60-75 cents a shot minimum. Now the question is, is it worth 75 cents a shot to have a .458 to plink with?
You bet your ass it is!