1999 Hydro Challenger Professional

I am looking to sell my B&R Hydro Challenger 11100m Professional. A lovely watch but I wear a more recent B&R auto so this one sits in a drawer most of the time. I purchased this new in July 1999 ref. 810.05071. Silicon filled, quartz movement 39mm case. Paperwork and original guarantee papers, spare links, no box or rubber strap. Recently serviced by B&R in Paris (certified). Full working order. I would appreciate guidance as to what these watches fetch these days, which will allow me to figure a realistic opening price on an auction site (any recommendations of where to sell). Thank you!