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

1. Current Condition: The coin has a condition 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. Previous Prices: Looking at previous auction prices, we can see that:
- In 2014, it was auctioned for 360 euros with an unspecified condition.
- In 2021, with a condition of 70, it was auctioned for 300 euros.
- In 2022, with a condition of 85, it was listed with a starting price of 900 euros, although it did not sell.
- In 2024, with a condition of 90, it was auctioned for 600 euros.

3. Starting Price and Average Price: The current starting price is 600 euros, and the average auction price in previous sales is 390 euros. This suggests that the starting price is aligned with collectors' expectations.

4. Sales Trends: Out of the 10 previous auctions, 8 resulted in sales, indicating a consistent interest in this coin.

Based on these factors, an estimated maximum purchase price could be in the range of 700 to 800 euros, considering that the condition is good and there has been interest in the past. This also takes into account the current starting price and previous auction prices.