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

1. Starting price: 75 euros.
2. Current condition: 50 (fine), indicating an acceptable but not excellent condition.
3. Auction history:
- In 2021, the coin was auctioned with an estimated price of 70 euros and sold for 121 euros, indicating significant interest in that auction.
- In 2024, it was auctioned with a starting price of 125 euros and sold for 125 euros, suggesting that interest may have decreased or that the condition was similar.

4. Average hammer price: 107 euros, which is a good indicator of market value.

Given that the current condition is 50 and considering that the average hammer price is 107 euros, we can estimate that the maximum purchase price could be in a range between the starting price and the average hammer price.

Taking all these factors into account, an estimated maximum purchase price could be around 100-110 euros. This is based on the interest shown in previous auctions and the average hammer price, adjusted for the current condition of the coin.