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 not in very good shape. This generally negatively affects its value compared to coins in better condition.

2. Auction History:
- The average hammer price for similar coins in the past is 103.67 euros.
- However, the highest recorded hammer price for a coin with a similar condition (25) was 21 euros in 2021 and 50 euros in 2024, suggesting that the value may be quite limited for coins in this condition.

3. Starting Price and Previous Prices:
- The current starting price is 25 euros, which is a good starting point.
- In previous auctions, the starting price has varied, but the highest hammer price for a condition of 25 was 21 euros.

4. Sales Trends: The coin has sold in 6 out of the last 7 auctions, indicating moderate interest in the coin, but the hammer price has been variable.

Based on these factors, an estimated maximum purchase price could be between 20 and 30 euros, considering that the condition is low and that previous hammer prices for coins in similar conditions have not exceeded 50 euros.

Therefore, a reasonable maximum purchase price could be 30 euros.