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

1. Current Condition: The coin has a condition of 30 (BC+), which indicates that it is not in the best condition. This will affect its value compared to coins in better condition.

2. Historical Prices: By looking at the auction 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 70, 80, 90, 95) have reached auction prices ranging from 8 euros to 190 euros.

3. Average Auction Price: The average auction price for this coin is 54.06 euros, which gives us an idea of what buyers are willing to pay on average.

4. Starting Price and Average Starting Price: The current starting price is 18 euros, and the average starting price is 34.08 euros. This suggests that the starting price is relatively low compared to the average auction price.

5. Sales Trends: The coin has been auctioned 38 times, of which it has sold 32 times. This indicates a consistent interest in the coin, which may influence its price.

Given all this, and considering that the coin's condition is 30 (BC+), an estimated maximum purchase price could be in the range of 30 to 50 euros. This is based on the fact that, although the condition is not high, the interest in the coin and historical prices suggest it could reach a reasonable price at auction.

Therefore, an estimated maximum purchase price could be 40 euros.