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

1. Starting price: 50 euros.
2. Current condition: 75 (MBC), which is a good condition.
3. Auction history:
- In 2013, it was auctioned with a starting price of 80 euros and sold for 80 euros.
- In 2016, it was auctioned with a starting price of 30 euros, sold for 40 euros, and the condition was also 75.
- In 2024, it was auctioned with a starting price of 30 euros, estimated at 50 euros, and sold for 80 euros, with a condition of 80.

4. Average hammer price: 66.67 euros, indicating that, in general, coins of this reference tend to sell above their starting price.

Given that the condition of the coin at auction is 75, which has shown good performance in the past, and considering that the average hammer price is 66.67 euros, we can estimate a maximum purchase price.

Taking into account the price history and the condition, a reasonable maximum purchase price could be in the range of 80 to 90 euros, as this aligns with the highest hammer price observed and the trend of previous auctions.

Maximum purchase estimate: 85 euros.