This forum is focused on competitive shooting, now collecting. That said, your P226, while a great gun, is nothing special. They are plentiful and not really a collector, especially one that's already been shot. I'd probably give you $600 tops if it's all original, but you said it has replacement grips and sights, to that drives the value way down to probably $400 or so. OBTW, W. German Sigs had proof marks, so nothing special about that.
You are going to be disappointed that your gun isn't as valuable as you think or where hoping it to be. Just shoot it and enjoy a truly classic gun.