Unless it's 'Like New In Box' and unfired, I'd fire it, but like Bret said, don't use it as a beater.
I was a little shocked at those GB auction prices also, but I also know Steyr Maadis were $2500 before the scamdemic panic.
I'd personally not shoot the corrosive through it, but that's just my OCD. Kind of like running Walmart brand oil in your Ferrari. Sell the case of ammo. No expert, but I'd bet that's steel core (no AP though) and some people will pay a premium for it because there is no more being imported. You might be able to buy 1.5 - 2x as much non-corrosive ammo for what you get for it.