Value for 4.5L Teacher's Whisky?

Hi, back in the late 1970's early 1980's I was given a 4.5 litre bottle of Teacher's Whisky. I still have this bottle unopened. An empty bottle was selling for $90.00 on Gumtree.com so I would like to know the value of my full one please? I wish to sell it on ebay shortly. Thank you