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

1. Coin Condition: The coin has a condition rating of 25 (BC), which indicates that it is not in very good shape. This generally reduces its value compared to coins in better condition.

2. Auction History: By observing the hammer prices of similar coins in the past, we can see that prices vary significantly depending on the condition. For example, coins with higher grades (such as 80 or 90) have reached hammer prices of up to 190 euros.

3. Starting Price and Previous Prices: The current starting price is 15 euros, and the average hammer price in the past for similar coins is approximately 98.9 euros. However, given that the condition of this coin is low, it is likely that the hammer price will be below the average.

4. Recent Trends: In recent auctions, hammer prices for coins in similar conditions have ranged between 30 and 50 euros, depending on demand and rarity.

Taking all these factors into account, an estimated maximum purchase price for this coin, considering its condition and auction history, could be between 25 and 40 euros. This reflects a balance between the state of the coin and previous hammer prices for coins of similar condition.