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 fairly good shape, but not the best possible condition.

2. Auction History:
- The coin has been auctioned 6 times and has sold on all occasions, indicating a consistent interest in the coin.
- The average hammer price in previous auctions is 57.61 euros, which can serve as a reference for the expected selling price.

3. Previous Prices:
- In 2013, the coin sold for 82 euros at auction, which is a notably high price compared to other hammer prices.
- In 2014, it sold for 66.04 euros at auction with a condition rating of 90, suggesting that better condition can increase the price.

4. Starting Price: The current starting price is 50 euros, which is a good starting point.

Given that the coin's condition is 75 and considering the price history, an estimated maximum purchase price could be in a range between the average hammer price (57.61 euros) and the highest recorded price (82 euros).

Taking all these factors into account, a reasonable estimated maximum purchase price could be around 70-75 euros. This reflects interest in the coin, its condition, and the price history in previous auctions.