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

1. Current Condition: The coin has a condition rating of 30 (BC+), which indicates that it is not in the best condition. This generally reduces its value compared to coins in better condition.

2. Historical Prices: By looking at the auction prices of coins with a similar condition (30) in the past, we can see that the auction prices have varied. For example, in previous auctions, coins with a condition of 30 have reached hammer prices ranging from 10 to 20 euros.

3. Average Hammer Price: The average hammer price for this particular coin is 98.02 euros, but this includes coins in better condition. Therefore, it is not a good indicator for our specific coin.

4. Starting Price: The starting price is 15 euros, which can be a good starting point for the auction.

5. Recent Trends: In the most recent auctions, hammer prices for coins with similar conditions have been in the range of 20 to 35 euros.

Taking all these factors into account, an estimated maximum purchase price for this coin, considering its condition and historical prices, could be between 20 and 30 euros. This reflects a balance between the condition of the coin and previous hammer prices.