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

1. Current Condition: The coin has a condition rating of 90 (EF), indicating that it is in quite good shape. This generally translates to a higher price compared to coins in lower conditions.

2. Auction History:
- The average hammer price in the past has been 43.81 euros.
- The last auction of a coin with a similar condition (95) had a hammer price of 160 euros, suggesting that coins in very good condition can reach high prices.
- Overall, hammer prices have varied, but there are examples of coins with similar conditions that have sold for significantly higher prices.

3. Starting Price and Estimates:
- The current starting price is 40 euros, which is a good starting point.
- The average starting price in the past has been 37 euros, indicating that the current starting price is reasonable.

4. Price Trends:
- Since the coin has been auctioned 23 times and has had a sell-through rate of 95.65% (22 out of 23), this suggests there is consistent interest in this coin.

Based on these factors, an estimated maximum purchase price could be in the range of 70 to 90 euros, considering that the condition is good and there are precedents of higher hammer prices in the past. However, given the auction history and interest in the coin, a maximum purchase price of 80 euros could be a reasonable estimate.