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

1. Starting Price: 2500 euros. This is the initial price set for the auction.
2. Condition: The coin has a condition rating of 95 (S/C-), indicating that it is in very good shape. This generally increases its value.
3. Auction History:
- In the December 2021 auction, the coin was estimated at 1500 euros and sold for 3200 euros, indicating significant interest in this reference.
- In the June 2022 auction, although no final prices were provided, the starting price was 6000 euros, suggesting that the seller had high expectations, although the sale did not materialize.

4. Average Hammer Price: 1660.5 euros, which is an important figure for understanding the average value of the coin in the market.

5. Average Starting Price: 4250 euros, which is considerably higher than the current starting price of 2500 euros.

Given that the coin is in good condition and has shown interest in previous auctions, an estimated maximum purchase price could be in a range above the starting price, but also considering the average hammer price.

Taking all these factors into account, an estimated maximum purchase price could be between 3200 and 4000 euros, as this reflects both the interest shown in previous auctions and the good condition of the coin.

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