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

1. Starting Price: 100 euros. This is the initial price set for the auction.
2. Condition: The coin has a condition rating of 85 (ebc-), indicating that it is in fairly good shape. This generally increases its value compared to coins in lower condition.
3. Auction History: The coin has been auctioned 2 times in the past, of which it sold 1 time and did not sell 1 time. This suggests that there is interest in the coin, but also that there may be a limit to what buyers are willing to pay.
4. Previous Prices: In the 2015 auction, the starting price was 39.91 euros and the final price was the same, indicating that there was no significant increase in price on that occasion.

Given that the current starting price is 100 euros, which is considerably higher than the previous final price, and considering the condition of the coin, an estimated maximum purchase price could be in a range between the starting price and the average final price of previous auctions.

Taking all these factors into account, an estimated maximum purchase price could be approximately 70-80 euros. This is based on the potential interest of buyers, the condition of the coin, and the price history.