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

1. Condition: The coin has a condition rating of 80 (MS+), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History: The coin has been auctioned 3 times in the past and has sold on all occasions. This is a good indicator of demand and can positively influence the price.

3. Previous Prices:
- In 2017, the coin was auctioned with a starting price of 18 euros and sold for 40 euros, with a condition of 70.
- In 2024, it was auctioned with a starting price of 20 euros and sold for 35 euros, also with a condition of 70.

4. Average Hammer Price: The average hammer price for this coin is 40 euros, suggesting that buyers are willing to pay close to this price in previous auctions.

5. Current Starting Price: The current starting price is 30 euros, which is reasonable given the price history and the condition of the coin.

Given that the condition of the current coin is better than the previous ones (80 versus 70), it is reasonable to assume that the hammer price could be higher than the average of 40 euros.

Taking all these factors into account, an estimated maximum purchase price could be between 45 and 50 euros, considering that the condition is better and there is a history of successful sales.