To estimate a maximum purchase price for the coin that will be auctioned, we can consider several factors, including the starting price, the condition of the coin, and the hammer prices of similar coins in the past.

1. Starting price: 25 euros.
2. Condition of the coin: 80 (MBC+), indicating good preservation.
3. Previous hammer prices:
- In past auctions, coins with a similar condition (80) have reached hammer prices that varied considerably, but some relevant examples are:
- 190 euros (condition 80)
- 60 euros (condition 80)
- 55 euros (condition 90)
- 48 euros (condition 85)
- 42 euros (condition 85)

4. Price trends: The average hammer price for similar coins is approximately 99.9 euros, suggesting that there is a market willing to pay more than the starting price.

5. Competition analysis: There are 18 similar coins that will be auctioned in the coming days, which may influence demand and the final price.

Based on these factors, an estimated maximum purchase price could be between 80 and 120 euros, considering that the condition is good and that the average hammer price is significantly higher than the starting price.

Therefore, a reasonable maximum purchase price could be 100 euros.