To estimate a maximum purchase price for the coin in question, let's consider several factors:

1. Starting Price: 5000 euros. This is the initial price set for the auction.
2. Auction History: The coin has been auctioned 3 times and has sold on all occasions. This indicates a consistent interest in the coin.
3. Previous Prices:
- In the December 2021 auction, the final price was 2200 euros with an estimated price of 3000 euros.
- In the December 2024 auction, the final price was 2600 euros with an estimated price of 3000 euros.
4. Condition: The coin has a condition rating of 95 (S/C-), indicating that it is in very good condition.

Since the starting price is significantly higher than the previous final prices (2200 and 2600 euros), it is likely that the starting price of 5000 euros is too high compared to the sales history. However, the good condition of the coin may justify a higher price.

Based on the average final price of previous auctions (approximately 2400 euros) and considering the condition, a maximum estimated purchase price could be between 3000 and 3500 euros. This is because, although the starting price is high, the condition and interest in the coin could allow for a final price higher than the previous ones, but not as high as the starting price.

Therefore, a maximum estimated purchase price could be 3500 euros.