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

1. Current Condition: The coin has a condition of 85 (MBC+/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 (85 and 80), we can see that the hammer price has varied but has reached significant figures. For example:
- In 2020, a coin with a condition of 85 was auctioned for 280 euros.
- In 2022, a coin with a condition of 85 was auctioned for 400 euros.
- In 2023, a coin with a condition of 95 was auctioned for 600 euros, indicating that the value may increase with better condition.

3. Starting Price and Average Hammer Price: The current starting price is 300 euros, and the average hammer price in the past has been 306.06 euros. This suggests that the hammer price could be in a similar or slightly higher range.

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

Based on these factors, an estimated maximum purchase price could be in the range of 400 to 450 euros, considering that the coin is in good condition and that hammer prices have been higher in recent auctions. This also takes into account the possibility that other bidders may be interested in the coin, which could drive up the final price.