Hi there Dubois,
Ardbeg 1977 is indeed a very good example of an Ardbeg, but the distillery has now run out of stock. This means the value is immediately rising as more people want one, either to drink or to add to their collections / investments.
During 2004 the typical price was anywhere from €81 to €102 as many were sold on Ebay and from shops.
Since late 2005 when it was announced that there was no more, the price has just about doubled. If you are lucky, it can still be found for around €130 to €150, but as Aidan has already said, more sellers are asking €170 to €200 for this.
Personally, I prefer the 1975 which came in three standard variants; bottled 1999, 2000 & 2001. These have held a steady price on the market for the last year at around €180 to €210, with just a couple reaching €250. So if I were looking to spend €180 to €200 on one of these to drink, I would choose the 1975.