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 (ebc-), which indicates that it is in fairly good shape, but not the best possible condition.

2. Previous Prices: Looking at previous auction prices for coins with similar conditions:
- In 2018, a coin with a condition of 85 was auctioned for 750 euros.
- In 2022, a coin with a condition of 95 was auctioned for 950 euros.
- In 2024, a coin with a condition of 90 was auctioned for 851 euros.

3. Average Auction Price: The average auction price for this coin in the past has been 869.28 euros, which gives us a good reference.

4. Current Starting Price: The starting price is 600 euros, which is a reasonable starting point.

5. Sales Trends: The coin has been auctioned 22 times, of which it has sold 18 times, indicating good demand.

Based on these factors, an estimated maximum purchase price could be between 850 and 950 euros, considering that the condition is slightly lower than the coins that have sold in that range. Therefore, a reasonable maximum purchase price could be 900 euros.