Because he's a club special run, so it would have cost the seller a lot to get him in the first place.
Ready? This might get complicated
To buy the Stablemates Club models, first you have to join the Breyer Collector Club, with a fee for the entire year.
Then you have to join the Stablemates Club, which is another fee (you can't join the second club without joining the first one, so there's no getting round paying twice).
Once in the clubs, you then have to buy the models they release in that year, most are compulsory - you have to buy them whether you like/want them or not - but some are optional extras for club members only, I just checked and he's one of those optional releases. He would've cost $20 new.
Now, this model's in Germany, which means they've also had to pay the expensive shipping to get him from the USA, quite likely getting extra customs/import/handling fees along the way.
So yeah, the price soon adds up to make these club special runs really pricey on the international resale market!