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

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

2. Current Listing Price and Previous Prices: The current listing price is 400 euros. In previous auctions, hammer prices have varied, but there are examples of sales that have exceeded 400 euros, especially for coins in similar or better conditions.

3. Price Trends: Looking at previous hammer prices, there are several cases where coins with similar conditions have reached hammer prices between 340 and 440 euros. This suggests that the market is willing to pay competitive prices for well-preserved coins.

4. Average Hammer Price: The average hammer price for this coin is 279.29 euros, but given that the current condition is above the average of auctioned coins, it is reasonable to expect a higher hammer price.

5. Sales Expectations: Since there are 3 auctions scheduled in the coming days, this may increase competition and, therefore, the hammer price.

Based on these factors, an estimated maximum purchase price could be between 450 and 500 euros. This is due to the good condition of the coin and the price trends in previous auctions. However, it is important to keep in mind that the final price will depend on the competition in the auction and the demand at that specific moment.