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 previous auctions.

2. Starting Price and Average Hammer Price: The current starting price is 450 euros, and the average hammer price in previous auctions is 315.14 euros. However, the starting price is higher than the average hammer price, which may indicate that the seller has higher expectations.

3. Price History: By looking at previous hammer prices for coins with similar conditions (85-90), we can see that hammer prices have varied, but there are examples where coins with a condition of 85 have reached hammer prices of up to 400 euros.

4. Recent Trends: In the most recent auctions, hammer prices have ranged from 390 to 550 euros for coins of similar condition. This suggests that there is growing interest in coins of good condition.

5. Estimation Based on Historical Data: Given that the coin has a condition of 85 and considering previous hammer prices, an estimated maximum purchase price could be in the range of 400 to 500 euros, depending on the demand at the auction.

Conclusion: Based on all these factors, an estimated maximum purchase price for this coin could be approximately 500 euros. This aligns with the highest hammer prices observed in the past for coins of similar condition.