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

1. Coin Condition: The coin has a condition of 85 (ebc-), which indicates that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History: By observing the hammer prices of coins with similar conditions (around 85), we can see that the hammer prices have varied. For example:
- In previous auctions, coins with a condition of 85 have reached hammer prices of up to 240 euros (as in the auction on 2018-04-25).
- There are also examples of coins with a condition of 80 that sold for 58 euros (auction on 2020-09-17) and 65 euros (auction on 2019-12-10).

3. Starting Price and Average Hammer Price: The current starting price is 75 euros, and the average hammer price in the past has been approximately 67.97 euros. This suggests that the starting price is reasonable and could attract bidders.

4. Recent Trends: In the most recent auctions, hammer prices have shown a tendency to be higher, especially for coins in good condition.

Based on these factors, an estimated maximum purchase price could be in the range of 150 to 200 euros, considering that the condition is good and there is a history of hammer prices that supports this estimate. However, since the starting price is 75 euros, it is likely that bidders will be willing to pay more, but they may not necessarily reach the estimated maximum unless there is significant competition in the auction.

Therefore, a reasonable maximum purchase price could be 150 euros.