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

1. Current Condition: The coin has a condition rating of 25 (BC), indicating that it is in fairly low condition. This generally reduces its value compared to coins in better condition.

2. Auction History:
- It has been auctioned 7 times in the past, of which it has sold 5 times. This indicates a moderate interest in the coin.
- The average hammer price from previous auctions is 331 euros, providing a benchmark for the coin's value.

3. Previous Hammer Prices:
- Previous hammer prices varied, but there are examples of hammer prices exceeding 300 euros, even with higher conditions.
- The last auction with a known hammer price was 340 euros with a condition of 80, suggesting that the value could be significantly higher in better conditions.

4. Current Starting Price: The starting price is 250 euros, which may be a good starting point for the auction.

Given that the coin's condition is low (25), it is likely that the hammer price will not reach the higher levels observed in coins of better condition. However, considering the interest in the coin and the price history, an estimated maximum purchase price could be around 200-250 euros, depending on the competition in the auction and the interest from collectors.

Therefore, an estimated maximum purchase price could be 250 euros.