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

1. Current Condition: The coin has a condition of 80 (MBC+), which indicates 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 has been 76.7 euros.
- In previous auctions, the hammer price has varied, but there are examples of sales reaching up to 400 euros (in the case of a condition of 95).
- The last auction with a similar condition (80) had a hammer price of 50 euros.

3. Starting Price and Average Starting Price: The current starting price is 40 euros, which is consistent with the average starting price of 40.64 euros.

4. Sales Trends: Out of the 25 times it has been auctioned, 21 have resulted in sales, indicating good demand.

Based on these factors, an estimated maximum purchase price could be in the range of 80 to 100 euros, considering that the condition is good and the average hammer price is 76.7 euros. However, since the market can be volatile and depends on demand at the time of the auction, a prudent maximum purchase price could be 90 euros. This allows for a margin to compete in the auction without exceeding the historical hammer value.