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 75 (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: By looking at previous hammer prices for coins with similar conditions (75 and 80), we can see that:
- In past auctions, hammer prices for coins with a condition of 75 have ranged between 25 and 80 euros.
- The average hammer price for coins with a condition of 75 seems to be around 40-60 euros.

3. Starting Price and Average Hammer Price: The current starting price is 25 euros, and the average hammer price in the past has been 43 euros. This suggests that the hammer price could be higher than the starting price.

4. Auction Trends: Given that the coin has been auctioned 18 times in the past and has had a good sales percentage (14 out of 18), this indicates a consistent interest in the coin, which may increase its value.

5. Estimation Based on Previous Prices: Considering that the highest hammer price for a coin with a condition of 75 was 80 euros, and that the average hammer price is 43 euros, we can estimate that a reasonable maximum purchase price could be in the range of 60-80 euros.

Conclusion: Based on all these factors, an estimated maximum purchase price for the coin in question could be approximately 70 euros. This sits at a midpoint between the average hammer price and the highest observed hammer price, taking into account the current condition of the coin.

Based on the provided data, the coin in question has a conservation grade of 75 (MBC) and has had a consistent starting price of 25 euros in previous auctions, with a hammer price also of 25 euros. This indicates that, despite the estimated price being 40 euros, there has been no increase in the hammer price in past auctions.

Since the coin has been auctioned twice and has reached the same hammer price on both occasions, it is reasonable to assume that interest in this coin has not increased significantly. Furthermore, the fact that it will be auctioned again shortly suggests that the market has not changed drastically.

Therefore, a maximum estimated purchase price could be slightly higher than the previous hammer price, but not by much, given that interest seems to be stable. An estimated maximum purchase price could be around 30-35 euros, considering a small margin for competition in the auction.

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

1. Condition: The coin has a condition rating of 85 (ebc-), 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 in previous auctions is 79.13 euros, suggesting that, in general, coins of this reference tend to sell for significantly higher prices than the starting price.
- In past auctions, we have seen hammer prices vary, with some reaching up to 300 euros in 2011, although this may be an exceptional case.

3. Starting Price and Estimated Prices:
- The current starting price is 25 euros, which is relatively low compared to the average hammer price.
- The estimated price in previous auctions has varied, but there are examples where prices have been estimated at 40 to 50 euros.

4. Recent Trends:
- In the most recent auctions, the hammer price has been 40 and 120 euros for coins with the same condition, indicating a growing interest or an upward trend in the value of these coins.

Based on these factors, an estimated maximum purchase price could be in the range of 80 to 120 euros, considering the average hammer price and the condition of the coin. However, given the history of hammer prices, a reasonable maximum purchase price could be approximately 100 euros. This allows for competition in the auction and reflects the value of the coin's condition.