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

1. Current Condition: The coin has a condition of 25 (BC), indicating that it is in a fairly deteriorated state. This will negatively affect its value compared to coins in better condition.

2. Previous Prices: By observing the auction prices of similar coins in the past, we can see that prices have varied considerably. Coins with higher conditions (70, 80, 85) have reached auction prices ranging from 120 to 280 euros.

3. Starting Price and Average Hammer Price: The current starting price is 160 euros, and the average hammer price in previous auctions is 176.39 euros. This suggests that the market is willing to pay a little more than the starting price, but this also depends on the condition.

4. Auction Trends: The coin has been auctioned 19 times and has sold every time, indicating a consistent interest in this reference. However, the current condition is a limiting factor.

Given that the condition of the coin is low (25), and considering the hammer prices of coins in better condition, an estimated maximum purchase price could be set at a lower range than the average hammer price of coins in better condition.

Estimated Maximum Purchase Price: Based on the above information, a reasonable maximum purchase price could be between 100 and 130 euros. This reflects the low condition and the interest in the coin, but also considers that the hammer price could be lower due to its state.