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

1. Current 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. Current Starting Price and Previous Prices: The current starting price is 900 euros. In previous auctions, the average hammer price has been 296.17 euros, but there have also been auctions that exceeded 1,000 euros, especially for coins in good condition.

3. Historical Trends: By observing the hammer prices of coins with similar conditions (around 80-85), it can be noted that prices can vary significantly. For example, in previous auctions, some coins with a condition of 80 have sold for up to 1,600 euros.

4. Demand and Supply: The coin has been auctioned 52 times in the past, with a sell-through rate of 88.5%. This suggests that there is consistent interest in this coin, which may increase its value at auction.

5. Estimated Price: The estimated price of 400 euros in previous auctions for coins of similar condition is also a relevant data point.

Taking all these factors into account, an estimated maximum purchase price could be between 1,200 and 1,500 euros, considering that the condition is good and there is a history of high prices in previous auctions. However, the starting price of 900 euros also suggests that there may be opportunities to purchase at a lower price if competition is not high.