2 Euros is as cheap as chips depending on who wanted it over here it would go for @$80 - $120+/Aud thats only a rough guide get two "I want it's" and it could go for $200+.
I have seen stuff that well defies logic for ppl to pay that much but in a bidding war some just won't stop.
Just like $4,000/Aud for a Tiger 88mm round it was around for a while went to usedguns for a while then disappeared from the net so they may have sold it may not have, 15 years ago I was offered one for $1000/Aud at a show but turned it down as I only had that amount for the show.
I know what you mean on getting two people that want it in a bidding war haha. For a very long time, I had been looking for an m13 spam can of grenade cartridges that had the m3s, the m6s and the M7 booster cartridges(A little bit of everything). Well finally one showed up on gun broker and I got into a bidding war with another guy and I ended up paying $850 for it haha. Of course I way overpaid for it but they come along so very rarely, me and my son had already decided it was coming home to our collection before the auction had even ended regardless of what it was going to go for. Depends on how bad people want it. If things like this 20 mm anti-aircraft shell is very rare in your neck of the woods, I could easily see it reaching your estimate and then some