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

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

2. Auction History:
- The average hammer price for similar coins has been 52.95 euros.
- In previous auctions, coins with a similar condition (85) have reached hammer prices that varied, but some have gone up to 95 euros (as in the auction on 2020-09-17).

3. Starting Price and Estimates:
- The current starting price is 50 euros, which is reasonable given the history of hammer prices.
- The estimated price for this auction is 80 euros, suggesting that bidders are willing to pay more than the starting price.

4. Sales Trends: The coin has been auctioned 142 times, with a high sales percentage (121 out of 142), indicating consistent demand.

5. Comparison with Previous Prices: In past auctions, coins with a condition of 85 have had hammer prices ranging from 40 to 95 euros, depending on demand and other factors.

Based on these points, an estimated maximum purchase price for this coin could be between 80 and 100 euros, considering that the highest hammer price in the past for coins of similar condition has been 95 euros. Therefore, a reasonable maximum purchase price could be 90 euros.