To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin has a condition rating of 85 (ebc-), indicating that it is in quite good shape. This generally translates to a higher value compared to coins in lower condition.

2. Auction History:
- The coin has been auctioned 9 times in the past, of which it has sold 6 times. This suggests there is consistent interest in the coin.
- The average hammer price in previous auctions is 16.5 euros, providing a baseline for the expected value.
- The highest hammer prices in the past have been 25 euros (in 2020) and 20 euros (in 2022), indicating potential for reaching higher prices depending on demand.

3. Starting Price and Estimates:
- The current starting price is 30 euros, which is higher than the previous average hammer price. This may indicate that the coin is expected to reach a higher price due to its good condition.
- The average starting price in previous auctions is 16.11 euros, suggesting that the current starting price is quite optimistic.

4. Price Trends:
- Given that the condition is good and there is a history of hammer prices suggesting that the coin could reach higher prices, it is reasonable to consider that the hammer price could be in the range of 20 to 30 euros, depending on competition in the auction.

Based on these factors, an estimated maximum purchase price could be between 25 and 35 euros. This takes into account the good condition of the coin and the demonstrated interest in previous auctions. However, since the starting price is 30 euros, it is likely that the hammer price will not significantly exceed this value unless there is strong competition. Therefore, a prudent maximum purchase price could be 30 euros.