Based on the provided data, the coin in question has a grade of 80 (MBC+), has been auctioned once in the past and was sold on that occasion. The starting price in this auction is 18 euros, and the average selling price in previous auctions was 40 euros.

Given that the coin is in relatively good condition and has performed well in previous auctions, it is likely that its selling price in this instance will be higher than the previous average price. Taking these factors into consideration, as well as the fact that the coin sold in its only previous auction, we could estimate a maximum purchase price around 50-60 euros. However, it is important to note that the final price will depend on the demand at the auction and other potential interested buyers.