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

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

2. Previous Prices: By looking at previous auction prices for coins with a similar condition (85), we can see that they have reached auction prices of up to 480 euros (in the auction on January 18, 2024) and 340 euros (in the auction on June 1, 2022).

3. Starting Price and Average Hammer Price: The current starting price is 375 euros, and the average hammer price in the past has been 321.5 euros. This suggests that the starting price is reasonable and could attract bidders.

4. Auction Trends: The coin has been auctioned 22 times, with an 86% sell-through rate (19 out of 22). This indicates a consistent interest in the coin, which may influence the price.

5. Price Estimates: The estimated hammer price in previous auctions has varied, but it has reached significant figures. The most recent auction with a hammer price of 480 euros suggests that there is potential for the hammer price to be high.

Based on these factors, an estimated maximum purchase price could be around 450-500 euros, considering that the interest in the coin and its condition are favorable. This would allow for competitive bidding in the auction without exceeding a reasonable limit based on the price history.