.380 Automatic (also known as 9mm Kurz and 9x17mm) has been a somewhat oddball handgun caliber until just a few years ago. There were a few guns sold in 380, such as the Kel Tec P3AT and a couple of offerings from beretta and Taurus, but the popularity of the .380 has gone way up in the last few years. Why? Right to carry.
Many states have adopted legislation allowing people to get concealed permits. With this, there's been a huge thirst in the market for small, concealable pocket-sized guns. Since there is a general consensus among firearms enthusiasts that .380 is the bare minimum (debatable) for defensive shooting situations, the demand for small guns in this caliber has skyrocketed.
In just the past few years, guns such as the Ruger LCP, I.O. Hellcat, Magnum Research Micro Eagle, Diamondback DB, Taurus TCP, and Sig 238 have come on the market, all chambered in .380. Because of this, the once somewhat obscure cartridge has had a surge in demand, which has caused ammo prices for this particular caliber to go through the roof.
The .380 is the perfect storm. Why? because of its ballistic profile. Using ball ammunition, the round penetrates extremely well in a defensive situation (such as being fired from a relatively short barrel and impacting a target covered in a few layers of clothing). The problem is that it penetrates too well. On the other hand, when hollowpoints are implemented, their expansion is iffy at best. Which would you like when carrying your favorite 380? overpenetration (which endangers those other than your intended target) or questionable penetration? take your pick.