That's a great price nowadays... would even be a decent price pre-panic. I've seen advertisements for 1000 rounds as high as $400-500
Funny thing about that is, I asked the guy early when I first got there how much and he said $10 a box (20 rds). Later that afternoon I walked by him holding the SKS stock I bought. I don't think he remembered me. He asked me if I needed some ammo for my SKS, I said if you got any for $5 a box I will take 10. He jumped on it.
My guess is he was getting sick of people walking away when he quoted $10