The price depends strongly on condition; in mint condition with original packaging 1,200–1,300 euros were named. The Vermeil variant is equipped with blue sapphires; only the gold version limited to 4,810 pieces carries rubies, in distinction from the 30,000 standard edition in sterling silver with rubies. Reliable indications are provided by ended auctions national and international (especially eBay), with ultimately the current supply-demand state deciding. The market for such editions is dynamic; a sale at currently weak dollar is not currently recommended.
Related pages on fountainpen.de:
• Montblanc Writers Edition Agatha Christie (1993): https://www.fountainpen.de/writer-christie-en.htm