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

1. Current condition: The coin has a condition of 25 (BC), which indicates that it is not in very good shape. This will negatively affect its value compared to coins in better condition.

2. Auction history: The coin has been auctioned 3 times and has sold on all occasions. This suggests that there is interest in the coin, which may help maintain its value.

3. Previous prices:
- In the auction on April 28, 2022, the coin had a starting price of 30 euros and sold for 45 euros, with a condition of 30.
- In the auction on April 27, 2022, the starting price was 50 euros and it sold for 70 euros, with a condition of 75.

4. Average hammer price: The average hammer price of 55 euros is a good indicator of the value that buyers are willing to pay.

Given that the current condition is significantly lower than in previous auctions, the hammer price will likely be below the average of 55 euros. However, since there has been interest in the coin and it has sold in the past, we can estimate a maximum purchase price.

Taking all these factors into account, an estimated maximum purchase price could be between 30 and 40 euros, with 40 euros being a reasonable upper limit considering the interest in the coin and its sales history.