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

1. Current 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. Historical Prices: By looking at previous auction prices for coins with similar conditions, we can see that:
- In past auctions, coins with a condition of 85 have reached hammer prices of up to 400 euros.
- The last auction with a condition of 85 had a hammer price of 495 euros.

3. Starting Price and Average Price: The current starting price is 425 euros, which is above the average starting price of 270.09 euros and the average hammer price of 307.05 euros. This suggests that there is an expectation for the coin to sell at a higher price.

4. Recent Trends: In the most recent auctions, hammer prices have been on the rise, which could indicate a positive trend in the value of this coin.

Based on these factors, an estimated maximum purchase price could be around 450-500 euros, considering that the highest hammer price for a coin of similar condition was 495 euros. This also takes into account the current starting price and the trend of increasing hammer prices.