This bottle has sold on Whisky Auction between 2006-2010 ranging from 176-320 Euros. The two bottles sold earlier this year went for 253 and 245 Euros.
It's sometimes hard to value bottles based on whisky retailers because there can be a large difference in selling price.
There is a 1973/23 yr Rare Malt - 57.1% at TWE for 125 GBP, though not an exact comparison to your bottle.
Master of Malt has your bottle for 229.95 GBP.
Since you would have to pay fees to put it on auction and pay for shipping yourself, you could probably expect to make just under 200 Euros, give or take a little either way, depending on bids and fees. Private party sale would be less than auction, unless you find someone that really wants it.
Just my opinion...hope it helps.