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

1. Current Condition: The coin has a condition rating of 85 (MBC+/EBC-), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History:
- The average hammer price in previous auctions is 348.13 euros.
- The coin has been auctioned 13 times, of which it has sold 8 times, indicating good demand.
- In recent auctions, such as the one in December 2022, an estimated price of 600 euros was suggested, although it did not sell.

3. Starting and Hammer Prices:
- In previous auctions, starting prices have varied, but the current starting price is 300 euros.
- In the March 2023 auction, the hammer price was 300 euros with a condition of 75, suggesting that the hammer price could be similar or slightly higher for a coin in better condition.

4. Price Trends:
- The trend in hammer prices appears to be increasing, especially for coins in good condition.

Based on these factors, an estimated maximum purchase price could be between 400 and 450 euros, considering that the condition is good and that the hammer price history suggests buyers are willing to pay more for coins in similar conditions.

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