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

1. Current Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in relatively good shape. This suggests that its value should be above that of coins in worse conditions.

2. Auction History:
- The average hammer price for this coin in the past has been 91.77 euros.
- Coins with the same condition (80) have reached hammer prices of up to 312.13 euros in the past.
- The last auction of a similar coin with a condition of 80 had a hammer price of 75 euros.

3. Starting Price: The current starting price is 25 euros, which is quite low compared to previous hammer prices.

4. Price Trends: Looking at past hammer prices, there is a trend for coins in good condition (like the one with a condition of 80) to sell for over 100 euros on many occasions.

Based on these factors, an estimated maximum purchase price for this coin could be between 100 and 150 euros, considering that the average hammer price is 91.77 euros and there are examples of previous sales exceeding 300 euros.

Therefore, a reasonable maximum purchase price could be 150 euros.