To estimate a maximum purchase price for the coin that is going to be auctioned, we can consider several factors:

1. Condition of the coin: The coin in question has a condition of 85 (ebc-), which indicates that it is in fairly good shape, but not the best possible condition.

2. Previous auction prices: By observing the hammer prices of coins with similar conditions (85 and 90), we can see that the hammer prices have varied. For example:
- In previous auctions, coins with a condition of 85 have reached hammer prices of up to 391 euros (in 2023).
- Coins with a condition of 90 have reached hammer prices of up to 480 euros.

3. Average hammer price: The average hammer price for this coin is 325.76 euros, which gives us an idea of what buyers are willing to pay on average.

4. Starting price: The starting price of the auction is 425 euros, indicating that the seller expects a higher price than the average.

5. Recent trends: In the most recent auctions, hammer prices have been in a range of 391 to 440 euros for similar conditions.

Based on these factors, an estimated maximum purchase price could be set in a range between 400 and 450 euros, considering that the starting price is 425 euros and that the hammer price in previous auctions has been higher on occasions.

Therefore, a reasonable maximum purchase price could be 450 euros.