Like what Cargo said, $500 is a good deal. Consider also complete shelves, working locks with keys and lights. I paid $600 for mine and got to meet an Oakley brother.
The black ones are the newest display cases, they go for more, the x-metal looking display cases you can get cheaper. The pro to the the black ones is the lighting is better, but I like the style of x-metal better. I hope that helps out.
I bought one for $825. I know, I know it's more than I should have spent but it was mint. Looks brand new. Key included. Lights work. How old is that style of display case?