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 30 (BC+). This indicates that it is not in very good shape, which generally negatively affects its value.

2. Historical Prices: By looking at the auction prices of coins with similar conditions, we can see that the hammer prices for coins with conditions of 30 or close have varied. For example, in previous auctions, coins with a condition of 30 have had hammer prices ranging between 15 and 25 euros.

3. Starting Price and Average Price: The current starting price is 12 euros, and the average hammer price in the past has been 72.36 euros, but this includes coins in better conditions. Given that the condition of this coin is lower, it is unlikely to reach that average price.

4. Sales Trends: The coin has been auctioned 197 times, of which it has sold 163 times. This indicates good demand, but the hammer price will depend on the condition.

5. Comparison with Previous Prices: In previous auctions, coins with a similar condition have had hammer prices ranging between 15 and 25 euros.

Based on these factors, an estimated maximum purchase price for this coin, considering its condition and historical prices, could be between 20 and 25 euros. This reflects a balance between demand, condition, and previous hammer prices.