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 30 (BC+), indicating that it is not in the best shape. This generally reduces its value compared to coins in better condition.

2. Historical Prices: By looking at the hammer prices of similar coins in the past, we can see that prices have varied considerably. For example:
- In previous auctions, coins with similar conditions have reached hammer prices ranging from 40 to 150 euros, depending on demand and other factors.

3. Starting Price and Average Hammer Price: The current starting price is 18 euros, and the average hammer price in the past has been 131.63 euros. However, since the condition of this coin is below the average of those that have been auctioned, it is likely that the hammer price will be lower.

4. Recent Trends: In the most recent auctions, hammer prices for coins with similar conditions have been around 70-95 euros.

Taking all these factors into account, an estimated maximum purchase price for this coin could be around 70-90 euros. This reflects a balance between the current condition and historical prices, as well as recent market trends.