Based on the data provided, we can observe that the coin in question has had varying starting and final prices in previous auctions. The current condition of the coin is estimated at 30 (BC+), indicating that it is not in the best condition, but it is also not in the worst.

The average starting price in previous auctions was 53.83 euros, while the average final price was 71.11 euros. The coin has been auctioned 12 times in the past, being sold in 9 occasions and not sold in 3 occasions.

Taking into account the previous prices of the coin, its current condition, and the fact that it has been sold in most of the previous auctions, we could estimate a maximum purchase price around 80-90 euros. Since the starting price this time is 18 euros, it is possible that the final auction price will be higher than the starting price, but it is difficult to predict exactly how much it could be.

In summary, an estimated maximum purchase price for this coin in the next auction could be around 80-90 euros, considering its price history and previous sales.