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

1. Current Condition: The coin has a condition of 85 (ebc-), indicating that it is in quite good shape. This suggests that its value should be in the upper range of coins with a similar condition.

2. Previous Prices: Looking at previous auction prices for coins with a condition of 85, we see that they have reached hammer prices of up to 90 euros in recent auctions. For example, in 2018, a coin with a condition of 85 was sold for 90 euros.

3. Average Hammer Price: The average hammer price for this coin is 64.35 euros, which also provides a reference point.

4. Auction Trends: The coin has been auctioned 36 times, of which 31 have sold. This indicates good demand and consistent interest in the coin.

5. Starting Price: The starting price is 15 euros, which is relatively low compared to previous hammer prices.

Considering all these factors, an estimated maximum purchase price for this coin could be in the range of 80 to 100 euros, given that the condition is good and there are precedents for hammer prices in that range.

Therefore, a reasonable estimated maximum purchase price could be 90 euros.