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 rating of 85 (ebc-), indicating that it is in quite good shape. This is important because coins in better condition tend to fetch higher prices.

2. Starting Price and Average Hammer Price: The current starting price is 300 euros, and the average hammer price in previous auctions is 269.43 euros. This suggests that the starting price is aligned with the market value.

3. Sales History: The coin has been auctioned 46 times, of which 42 have been successful sales. This indicates good demand and consistent interest in the coin.

4. Previous Prices: Looking at previous hammer prices for coins with similar conditions (85 and 90), we can see that they have reached hammer prices of up to 600 euros in the past. However, there are also lower prices, suggesting that the market can be variable.

5. Recent Trends: In the most recent auctions, hammer prices have ranged from 320 to 750 euros, indicating that there is potential for a higher hammer price in the future.

Based on these factors, an estimated maximum purchase price could be in the range of 400 to 500 euros, considering that the coin is in quite good condition and there is a history of hammer prices that supports this estimate.

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