To estimate a maximum purchase price for the coin in question, we can analyze 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 suggests that its value should be in the upper range of previous auctions.

2. Previous Auction Prices: Previous auction prices for coins with similar conditions (around 75 to 85) have varied, but the highest recorded price was 9500 euros in 2017. However, most auction prices for coins in the 75 condition range have been around 2400 to 4200 euros.

3. Average Auction Price: The average auction price for this coin is 4838.78 euros, providing a good reference point.

4. Starting Price and Average Starting Price: The current starting price is 2500 euros, and the average starting price in the past has been 3100 euros. This suggests that the current starting price is competitive.

5. Auction Trends: The coin has sold in 9 out of the last 10 auctions, indicating consistent demand.

Based on these factors, an estimated maximum purchase price could be in the range of 4000 to 5000 euros, considering that the condition is good and the average auction price is 4838.78 euros.

Therefore, a reasonable maximum purchase price could be 4500 euros. This allows for a margin for competition in the auction and reflects the coin's condition value.