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. Historical Prices: By looking at previous auction prices for coins with a similar condition (85), we can see that they have reached auction prices that vary considerably. For example, in past auctions, coins with a condition of 85 have reached hammer prices of up to 750 euros (as seen in the auction on March 12, 2020).

3. Average Hammer Price: The average hammer price for this coin is 315.21 euros, which provides a good reference point.

4. Starting Price: The current starting price is 250 euros, suggesting that the seller has reasonable expectations based on sales history.

5. Recent Trends: In the most recent auctions, hammer prices have shown a trend of being higher, especially for coins in good condition.

Taking all these factors into account, an estimated maximum purchase price for this coin could be around 600-700 euros, as this aligns with the highest hammer prices observed in the past for coins of similar condition and the trend of increasing prices in recent auctions.