Based on the provided data, we can observe that the coin in question has had different starting, estimated, and final prices in previous auctions. Additionally, it has been auctioned several times with an average preservation of 70 (MBC-).

The current starting price is 18 euros, and the historical average starting price is 44.75 euros, while the historical average final price is 55.6 euros.

Considering the coin's previous prices and its average preservation, as well as the fact that it has been auctioned 12 times in the past, we can estimate a maximum purchase price for this coin in the upcoming auction.

Given that the current starting price is 18 euros and the historical average final price is 55.6 euros, we could consider an estimated maximum purchase price around 60-65 euros, taking into account the preservation and historical demand for the coin.

It is important to note that the final auction price may vary depending on factors such as competition from other bidders, interest in the coin in that particular auction, among others.