Alright, I made a stupid mistake. I was replacing in the Tavern, updating the armor of all my characters and selling my bad armor.
I was using an Xbox controller, so you press left-trigger + 'A' to sell individual items. I was doing this for about 10 minutes and then I accidently pressed right-trigger +'A' which sells all my unlocked items in my item box.
I still have my client open and haven't left the tavern. Is there a way to undo or buyback these items? Does buying back have an increased cost compared to selling? If this isn't possible, what about my items like my portal gun?
I'm new to Dungeon Defenders and I'm not sure if I am missing something obvious.