Several different events- inflation, rising metal prices, high demand, and the dollar losing strength against foreign currency- all led to skyrocketing ammunition prices in the last couple of years. In some calibers, prices literally doubled- when you could find any ammunition at all! In the last few months, supply seems to have finally caught up with demand, and as prices have dropped somewhat, I have invested in my own ammunition store.
I was talking to a friend about this. He's a competitive long-distance shooter, and very active with shooters in his local area. His take on the situation mirrors mine- prices can only rise from here, and this is the time to buy if you can. Here are some links.
Aim Surplus does not have a very wide selection, but they can be a good source especially for military calibers and inexpensive foreign ammunition.
Georgia Arms has been a favorite source of mine for years. Much of their ammunition is a screaming deal, while a few of their offerings (some of their rifle hunting ammo in particular) can be bested by major manufacturer rounds.
Midway has a broad ammunition selection, though the loaded ammunition can frequently be found less expensively elsewhere. The major advantage they offer is the huge selection, including components for the handloader, they have available.
Sportsman's Guide was a company I used frequently when I was younger. I sometimes found very good deals on surplus items like East German coats, and I liked the ability to set up an account, and distribute the cost of a large purchase over a few months. Here's a link to their ammo.
I am not saying the sky is falling. I am saying it's good to have gear before you need it, instead of being forced to pay a premium for whatever's available when you need it right damn now.