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

1. Current Condition: The coin has a condition rating of 80 (MBC+), 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 average hammer price for similar coins in the past is 81.38 euros.
- The last auction for this coin had a hammer price of 75 euros with a condition of 75.
- In previous auctions, the hammer price has varied, reaching up to 170 euros in an auction with a starting price of 90 euros.

3. Starting Price and Estimates:
- The current starting price is 40 euros, which is slightly lower than the average starting price of 42.5 euros.
- The estimated price for this auction is 70 euros, suggesting that bidders may be willing to pay more than the starting price.

4. Sales Trends: Of the 9 times it has been auctioned in the past, it has sold 8 times, indicating good demand for this coin.

Based on these factors, an estimated maximum purchase price could be in the range of 90 to 110 euros, considering that the condition is good and that the price history shows that coins in similar conditions have reached higher prices in the past.

Therefore, a reasonable maximum purchase price could be 100 euros. This allows for a margin for competition in the auction, given that the average hammer price is 81.38 euros and there is potential for a higher price due to the good condition.