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 the best condition, which will affect its value.

2. Auction History:
- The average hammer price for similar coins has been 245.58 euros.
- In the past, coins with similar conditions (around 30) have been auctioned, and the hammer prices have varied. For example, in 2018, a coin with a condition of 30 was sold for 11 euros, while another with a condition of 80 was sold for 40 euros.

3. Price Trends:
- The current starting price is 12 euros, which is relatively low compared to the average hammer price.
- The coin has been auctioned 82 times, of which 78 have sold, indicating good demand.

4. Recent Hammer Prices:
- In recent auctions, hammer prices for coins with similar conditions have ranged between 10 and 65 euros.

Based on these factors, an estimated maximum purchase price for this coin could be between 30 and 50 euros, considering that the condition is not high and that the price history shows significant variations. This would allow for a competitive offer without exceeding the current market value.