I'd say about $200 + shipping for starters. It just depends on how fast you want to move it and how much you want for it. I have seen them listed on E-bay for anywhere from $200 to $300.
I was going to buy one but actually found one made by KK Audio that acts as an open back cabinet, closed back cabinet, and ported Thiele style cabinet. Mine has the EVM-12L in it and I only spent $120. I don't mind that it is not a true Mesa cabinet because of the versatility. I might recover the cabinet in tolex though because I hate carpet.
You might just list it on E-bay with a reserve set to what you want out of it. Let the auction run its course then if it doesn't sell then you will know what people are willing to pay and you can either second chance sell it or just relist it for free. Just a thought.