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

The average starting price in previous auctions has been 75.83 euros, while the average final price has been 126.8 euros. However, in the last auction where the coin was sold, the final price was 151 euros.

Considering the relatively low conservation state of the coin and taking into account the previous final prices, as well as the fact that it has sold in most previous auctions, we could estimate a maximum purchase price around 160-170 euros. This is considering that the final price in the last auction was 151 euros and the current starting price is 18 euros.

It is important to note that the final auction price will depend on various factors, such as demand at the time of the auction and the willingness of buyers to bid on the coin.