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

1. Current Condition: The coin has a grade of 25 (BC), indicating that it is not in very good condition. This generally reduces its value compared to coins in better condition.

2. Auction History:
- The average hammer price for coins of the same reference has been 107.29 euros.
- However, the hammer prices for coins with similar grades (25) have been significantly lower. For example, in previous auctions, the hammer prices for coins with grades of 25 and 30 have ranged from 15 to 30 euros.

3. Starting Price and Average Starting Price:
- The current starting price is 12 euros, and the average starting price is 54.55 euros. This suggests that the market has higher expectations, but the condition of the coin limits its appeal.

4. Recent Trends: In the most recent auctions, the hammer prices for coins with similar grades have been in the range of 19 to 30 euros.

Based on these factors, an estimated maximum purchase price for this coin, considering its condition and price history, could be between 25 and 30 euros. This reflects a balance between the state of the coin and previous hammer prices for coins in similar conditions.