A year-end party or Christmas party costs roughly €250 to €350+ per person ex. VAT for 250 to 500 guests. For 500 to 1,000 guests you should count on roughly €225 to €325+ per person. For 1,000 to 2,000 guests around €200 to €300+ per person. Above 2,000 guests around €150 to €200+ per person. All amounts excluding VAT.
In December many venues and suppliers charge a peak-period surcharge. Book early: the best venues are already full in June.