To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

1. Starting price: 80 euros.
2. Average hammer price: 85 euros, indicating that in the only previous auction, the coin sold for a price slightly higher than the starting price.
3. Condition: The coin has a condition rating of 85 (ebc-), which is a good state and may positively influence its value.
4. Auction history: The coin has been auctioned once and sold on that occasion, suggesting there is interest in it.

Given that the average hammer price is 85 euros and considering that the condition is good, an estimated maximum purchase price could be slightly higher than the average hammer price, but not too much, to avoid the risk of overpaying.

Therefore, an estimated maximum purchase price could be between 90 and 95 euros. This would allow for competition in the auction without exceeding a reasonable limit based on the price history and the condition of the coin.