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+), which indicates that it is not in very good 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 the hammer prices for coins with similar conditions (around 30) tend to be lower. For example, in previous auctions, coins with conditions ranging from 30 to 70 have had hammer prices ranging from 12 to 75 euros.

3. Starting Price and Average Hammer Price: The current starting price is 12 euros, and the average hammer price for similar coins is 101.08 euros. However, given that the condition of this coin is quite low, it is unlikely to reach the average hammer price.

4. Recent Trends: In the most recent auctions, the hammer prices for coins with similar conditions have been lower, suggesting that the market may be adjusting downward for coins in less than optimal conditions.

Based on these factors, an estimated maximum purchase price for this coin could be between 20 and 30 euros. This reflects a balance between the condition and historical prices, taking into account that collector interest may vary.