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

1. Current Condition: The coin has a condition rating of 90 (EF), indicating that it is in good shape. This generally increases its value compared to coins with lower conditions.

2. Auction History:
- The coin has been auctioned 24 times, of which it has sold 19 times. This suggests there is consistent interest in the coin.
- The average hammer price in previous auctions is 31.89 euros, which can serve as a good indicator of market value.

3. Previous Prices:
- In past auctions, hammer prices for coins with a similar condition (90) have varied. For example, in 2020, a coin with a condition of 90 sold for 18 euros, while another with a condition of 95 sold for 60 euros.
- The highest hammer price for a coin with a condition of 90 was 34 euros in 2022.

4. Starting Price and Estimates:
- The current starting price is 25 euros, which is relatively low compared to previous hammer prices.
- The average starting price in previous auctions is 31.21 euros, suggesting that the current starting price could be attractive to buyers.

Based on these factors, an estimated maximum purchase price could be between 35 and 45 euros. This is based on the historical interest in the coin, its good condition, and previous hammer prices. However, since the market can be volatile, it is advisable to keep an eye on the auction and the competition.