To estimate a maximum purchase price for the coin in question, let’s consider the following factors:

1. Starting Price: 40 euros. This is the initial price set for the auction.
2. Condition: The coin has a condition rating of 30 (BC+), indicating that it is in fairly low condition. This generally negatively affects the value of the coin.
3. Auction History: The coin has been auctioned once and sold on that occasion, suggesting that there is interest in the coin, although the final price has not been provided.

Since there are no previous final prices for this coin and considering its condition, the starting price of 40 euros may be a good starting point. However, given that the condition is low, it is likely that the final price will not be significantly higher than the starting price.

Taking these factors into account, an estimated maximum purchase price could be between 40 and 60 euros, depending on collector interest and competition in the auction. However, given the condition, it is more likely that the price will be closer to the lower end of this range.

Therefore, an estimated maximum purchase price could be 50 euros.