As moving isn't usually an option,,, and some folks aren't shooting enough to make reloading a practical choice,, I'll offer this.
Where you usually shop for ammo,,, create a good, working relationship with the owner of the store. Ask them to order the ammo you seek. Even leave them a deposit if necessary.
However,,, a lot depends upon the store. If you are dealing with a big box store like wally world,, that won't work. Also, if you only buy small quantities,, a small dealer has to buy in case lots,, so it may be cost prohibitive.
Inexpensive ammo only exists in places where freedom of commerce is allowed. When you have several businesses that sell the same types of products,, then costs are competitive. (It's called capitalism.) In places that have restrictions,,, (California,) things cost more because of the lack of free enterprise.
For 45 Colt ammo, quite often none of it is " cheaper .45 Colt range ammo " no matter where you go. UNLESS you happen to have a large SASS club nearby & even then,,, most folks reload.
Reloading is the ONLY way to achieve good ammo, at a very reasonable expense.
As for the 12 gauge stuff,, not as many sellers or reloaders in shotgun,, and especially the mini stuff. I'm no help with that. That's where you need to build a relationship with a dealer.