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

1. Condition: The coin has a condition rating of 80 (MBC+), 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 9 times, of which it has sold 8 times. This suggests there is consistent interest in the coin.
- The average hammer price in previous auctions is 69.71 euros, providing a good reference for market value.

3. Previous Prices:
- In past auctions, hammer prices have varied, but there is a notable price of 100 euros in an auction with a condition of 85, indicating that coins in better condition can reach higher prices.
- The last auction with a condition of 85 had a hammer price of 100 euros, suggesting that the price may increase with improved condition.

4. Starting Price: The starting price is 40 euros, which is relatively low compared to previous hammer prices.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 70 to 90 euros, considering that the condition is good and that interest in the coin appears to be high. A price of 80 euros could be a reasonable target, as it aligns with the average hammer price and the price trends in previous auctions.