(Well, we'll see if this post is allowed)
You've got pictures.
Save the packaging.
You paid via PayPal, right?
Contact the seller and tell him the situation. ALL contact should be via eBay messaging, not email.
See if he's going to make it right.
What right means to you might not be the same to me.
So, do you want to keep it with a broken case? Do you think
that's worth 50% of the price? Do you not want it at all?
Do you want a total refund? You need to know what it is you want.
Do NOT agree to send it back at your expense.
If you're not happy with the discussions, then file a claim with eBay as SNAD (Significantly Not As Described).
(I'd probably do this anyway.)
And then let the claim process run its course.
Also, was the payment via PayPal funded by a credit card or PayPal balance?
You will probably get all of your money back - as part of the charm of the whole package was the intact case - including shipping. And if you have to return it, that shipping cost as well.
Sorry for your disappointment, but there is always another machine out there if you don't want this one.
Good luck!