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

1. Coin Condition: The coin to be auctioned has a condition of 75 (MBC), which indicates that it is in relatively good shape, but not among the best qualities.

2. Previous Prices: By looking at the hammer prices from previous auctions for coins of similar condition (75 and 70), we can see that:
- In 2019, a coin with a condition of 75 was sold for 110 euros.
- In 2024, a coin with a condition of 70 was sold for 210 euros.
- In 2024, another coin with a condition of 85 was sold for 2400 euros, but this is an exceptional case and cannot be considered representative for a condition of 75.

3. Average Hammer Price: The average hammer price for coins of this reference is 649.6 euros, but this includes coins of different conditions, so it is not directly applicable to the condition of 75.

4. Starting Price: The starting price of 40 euros is quite low compared to previous hammer prices, suggesting there is potential for a significant increase in the final price.

5. Auction Trends: Since the coin has been sold on all previous occasions and there have been no failed attempts at sale, this indicates a consistent interest in the coin.

Based on these factors, an estimated maximum purchase price for the coin with a condition of 75 could be in the range of 150 to 250 euros, considering that the highest hammer price for a similar condition was 210 euros and that the starting price is low.

Therefore, a reasonable estimated maximum purchase price could be 200 euros.