Note than the band is a “replica” also (I’ll be kind).
IMO, the price is at least double what it should be. However, it looks to be in excellent original condition.
I found a similar watch that sold at auction for around €700.
https://www.catawiki.com/l/13067415-omega-seamaster-18-kt-gold-men-s-wristwatch-1961
However, this watch is not in good condition, so the one you are looking at should sell for more.
So I think we’ve established a range here.
Good luck with the negotiations.
gatorcpa