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 compared to coins in better shape.

2. Auction History: By observing the hammer prices of coins with similar conditions (around 30), we can see that the hammer price has varied. For example, in previous auctions, coins with a condition of 30 have reached hammer prices ranging from 15 to 25 euros.

3. Average Hammer Price: The average hammer price for this particular coin is 98.22 euros, but this includes coins in better conditions. Therefore, it is not a good indicator for our coin with a condition of 30.

4. Recent Starting and Hammer Prices: In the most recent auctions, the starting prices for coins with similar conditions have been between 10 and 18 euros, with hammer prices often not exceeding 25 euros.

5. Market Trends: Since the coin has been auctioned 81 times and has had a high sales percentage (75 out of 81), this suggests that there is a consistent interest in this coin, which may help maintain its value.

Based on these factors, an estimated maximum purchase price for the coin with a condition of 30 (BC+) could be in the range of 20 to 30 euros. This takes into account the interest in the coin, its condition, and recent hammer prices for similar coins.