Based on the data provided, we can observe that the coin in question has had varying starting and final prices in previous auctions. The current conservation grade of the coin is 25 (BC), indicating that it is not in the best condition.

The average starting price of previous auctions was 102.87 euros, while the average final price was 130.73 euros. However, it is important to note that the estimated price of the coin has varied significantly in previous auctions, ranging from 55 euros to 200 euros.

Given that the coin is in a conservation grade of 25 (BC) and considering the previous prices from past auctions, as well as the current starting price of 18 euros, we could estimate a maximum purchase price of around 150 euros. This estimation is based on the fact that the estimated price in previous auctions has reached that value, despite the coin not being in the best condition.

It is important to remember that the final auction price will depend on various factors, such as collectors' demand at that specific moment, so it is advisable to pay attention to the auction and adjust the offer accordingly.