I think it is a combination of several things. (BTW, Gander Mountain had it for $12.99/box last time I looked. I go there every couple months on the off chance they actually have something I want at a reasonable price.)
People coming late to AR's. They have GOT to have it, don't care the price. They buy the gun, some ammo, and then they are set as far as they are concerned. They want to have it to have it, no other reason. They don't shoot it, won't clean it, but they "have it in case they need it."
This kind of attitude lets the places jack up the prices, and once the Fudds are gone, they try to charge the rest of us that. Some see this as a seller's market, and they can charge whatever they want, even if the gun is just short of junk. As long as enough people are panicking and buying guns, ammo, mags, etc., before what they perceive as a ban coming in the next year or so, it will not stop.
I would like a precision bolt action rifle, and maybe a shotgun, but if I bought no more guns, I am OK with what I have. I am still getting some ammo, but I am in almost the same situation. More would be better, but what I have would be OK too. (Except maybe for .22lr, I still want a few more cases)