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

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

2. Previous Prices: By looking at the auction prices of coins with a similar condition (30) in the past, we can see that the hammer price has varied. For example:
- In previous auctions, coins with a condition of 30 have reached hammer prices of 15 to 20 euros.
- The last auction of a coin with a condition of 30 had a hammer price of 20 euros.

3. Average Hammer Price: The average hammer price for this coin is 67.1 euros, but this includes coins in better condition. Therefore, it is not a good indicator for our specific coin.

4. Starting Price and Estimates: The starting price is 12 euros, and the estimated price is 20 euros. This suggests that the market expects the coin to sell in a low range.

5. Market Trends: Given that there have been 112 sales of this coin in the past, and considering that the average hammer price for coins in similar conditions has been around 15 to 20 euros, we can infer that the interest in this coin is not very high, which may also influence the price.

Based on these factors, an estimated maximum purchase price for this coin could be between 20 and 25 euros, considering that the condition limits its appeal and that the hammer prices in previous auctions have been relatively low.