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

1. Current starting price: 125 euros.
2. Auction history: The coin has been auctioned 2 times and sold on both occasions, indicating a consistent interest in the coin.
3. Average starting and hammer price: The average starting price in the past was 92.5 euros and the average hammer price was 125.5 euros. This suggests that the hammer price may be a good indicator of the coin's real value.
4. Condition: The coin has a condition rating of 80 (MBC+), which is quite good and may positively influence its value.
5. Previous prices: In the 2017 auction, the starting price was 60 euros and the hammer price was 71 euros, indicating that interest in the coin has increased over time.

Given that the average hammer price is 125.5 euros and considering the good condition of the coin, an estimated maximum purchase price could be set slightly above the average hammer price, but not too far above the current starting price to avoid overpaying.

Therefore, an estimated maximum purchase price could be approximately 135-145 euros. This allows for some competition in the auction, but is also based on the price history and the condition of the coin.