The cheapest ammo on the market, except for 22 LR ammo, is 7.62x39 (AK-47 ammo), and 5.56 x 45 (.223 Remington) and both can be had now for 23 to 25 cents per round. You won't likely be plinking or practicing much with shotgun ammo, especially at 75 cents per round.
If available in California, seriously consider a new model Ruger Mini-14 Ranch rifle (which is scoped). Yes, it would be $200 to $300 more than a bottom of the line WalMart rifle, but the savings in ammo will make the package (rifle plus 1000 rounds) about the same. There is .223 ammo available which will not overpenetrate walls. The 25 cent per round ammo would also allow relatively cheap plinking and practice, though not as cheap as 22 LR ammo.
This is a good perspective. Thanks. One thing I’ve been wondering is, let’s say I want to buy a handgun and a rifle. Is there such a thing as having the same ammo for both of them? Following the KISS rule.