Based on the provided data, we can observe that the coin in question has had a starting price in the current auction of 18 euros and is in a conservation grade of 90 (EBC). Additionally, it has been auctioned in the past on several occasions, with closing prices ranging from 12 to 120 euros.

The average closing price of this coin has been 39.13 euros, and the average starting price has been 20.53 euros. We can also see that it has had estimated prices in previous auctions ranging from 15 to 100 euros.

Given the high conservation grade of the coin (90 EBC) and considering the previous closing prices, estimated prices in previous auctions, and the current starting price, we could estimate a maximum purchase price around 110 euros. This price would be in line with previous closing prices and the quality of conservation of the coin.