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

1. Starting Price: 150 euros.
2. Condition: The coin has a condition of 25 (BC), indicating that it is not in very good shape. This generally negatively affects the final price.
3. Auction History:
- In 2015, it was auctioned with a starting price of 300 euros and sold for 300 euros.
- In 2014, it was auctioned with a starting price of 120 euros and sold for 125 euros.
- In 2022, it was auctioned with a starting price of 200 euros and sold for 550 euros, but the condition of that coin was 75, which is significantly better than the current condition.

4. Average Starting and Final Prices: The average starting price is 192.5 euros and the average final price is 325 euros. However, these averages may be influenced by coins in better condition.

Given that the condition of the current coin is quite low (25), it is likely that the final price will not reach the levels of coins in better condition.

Taking all these factors into account, an estimated maximum purchase price could be positioned in a range between the starting price and the average final price, adjusted for condition.

Estimated Maximum Purchase Price: It may be reasonable to consider a maximum purchase price of around 200-250 euros, given that the condition limits the potential final price, but there is still interest in the coin.