Be as outraged as you want, but this is an example of a free market economy and scaling. Far more .45ACP is manufactured than is .380. Because there is "plenty" of .45 ammo, the demand is lower and the price is lower. The demand for .380 is high and the supply is low, so prices are higher.
Because less .380 ammo is manufactured, the maker has to charge more per unit to make it worth his while to make it at all. Otherwise he'd be better off just making more .45 ACP ammo and not disrupting his production line - which is a high cost. All this is simple business, but is often not understood by folks who have never owned or worked for a manufacturing company.
Of course, to make it "fair" for everyone, we could just have a government that regulates all pricing so that no consumer ever pays too much. Now that sounds like a great idea to me....
.