Based on the data provided, we can observe that the coin in question has had quite variable starting and closing prices in previous auctions. The current condition of the coin is estimated at 20 (BC-), indicating that it is not in the best condition.

The average starting price in previous auctions has been 106.63 euros, while the average closing price has been 189.12 euros. However, it is important to note that the current starting price is 18 euros, which is significantly lower than the historical average starting price.

Given that the coin has sold in all previous auctions, and considering its relatively low current condition, we could estimate a maximum purchase price around 120-140 euros. This takes into account the low current starting price and the average closing price of 189.12 euros.

It is important to remember that the final auction price will depend on the demand at the time of the auction and the willingness of buyers to bid on the coin in question.