I mostly shoot the just over 1 cent per shoot 22 Cal CPHPs and don't see any "need" to own a 177 or a 30 or anything else for that matter, but I enjoy shooting the 30 cals, particularly the Blitz and the Gauntlet. and I like the somewhat safer 177 for shooting in my yard plus my 177 Beeman is super quiet.
On the 30 cals, I shoot the NOE cast slugs most of the time and they cost me less than a penny a shot not including my time which I have plenty of. I can shoot the NOE slugs as they drop out of the mold with no sizing or lube. I may try some harder alloy slugs out of the NOE molds, but they will have to be sized. Those will be totally free, from my 30 year stash of wheel weights.
I am going to get a big bore airgun soon, not sure on the caliber, but probably at least 35/9mm and will shoot my own cast slugs in it exclusively at pennies per shot. I rarely shoot my 22 LRs anymore but with the ammo coming down to almost 4 cents a round lately, I may start up again.