What is your frame of reference? One-way from USA to Guatemala or Belize (2 countries over) is cheaper than €1300?

I would say you are lucky to have been offered a one way at all considering these are non-neighbor countries in different regions of europe and your drop-off location is a very sparsely populated remote area.

Geographically speaking there are 3 other countries and a sea in between when driving the most direct route. 1800km is a huge distance in europe. A short ferry ride is crossing a river in 5 minutes to me. €1300 seems a very good deal to me.