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

1. Current Condition: The coin has a condition rating of 75 (MBC), indicating that it is in relatively good shape. This can positively influence its value.

2. Auction History:
- It has been auctioned 11 times, of which it has sold 10 times. This suggests there is consistent interest in the coin.
- The average hammer price in previous auctions is 68.54 euros, which can serve as a good indicator of market value.

3. Starting and Hammer Prices:
- The current starting price is 50 euros, which is lower than the average hammer price from previous auctions. This could indicate a good buying opportunity.
- In previous auctions, hammer prices have varied, but there are examples of hammer prices exceeding 100 euros, especially for coins in higher conditions.

4. Price Trends:
- In 2016, a coin with the same condition sold for 101.3 euros, suggesting there is potential to reach higher prices in the future.

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 that interest in the coin appears to be solid. A price of 90 euros could be a reasonable target, as it is in the middle of this range and aligns with previous hammer prices.