It's a two year old phone, so there's no warranty.

There are equivalent phones in the same price point: Nokia x, xl, 630, 635 are all around €100

And, I paid (the equivalent of) €300 two years ago for a 64 GB, which may still be worth €100, but is still worth more than a 16 GB.

€70 maybe, but you'd expect the box, cable, charger & case. If it still had the original screen protector then, yes, €100.

Just phone: €50
+ box & bits €70
"new" €100