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

1. Condition of the coin: The coin has a condition rating of 95 (EBC+), indicating that it is in very good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction history:
- The average hammer price for this coin is 315.21 euros.
- In previous auctions, we have seen hammer prices that varied significantly, but some relevant examples are:
- In 2018, a coin with the same condition (95) was sold for 850 euros.
- In 2023, a coin with a condition of 95 was sold for 700 euros.
- The trend shows that coins in good condition tend to reach higher prices, especially if there is demand.

3. Starting price: The starting price of 400 euros is a good indicator of the seller's expectations, but the final hammer price could be significantly higher if there is interest.

4. Comparison with previous prices: By looking at previous hammer prices for coins with similar conditions, we can see that the price range can be quite broad, but the highest prices have exceeded 700 euros.

Based on these factors, an estimated maximum purchase price for this coin could be between 700 and 850 euros, given that there are precedents for sales in that range for coins of similar condition. However, since the starting price is 400 euros, it is likely that the final hammer price will be closer to the lower end of this range unless there is significant competition in the auction.

Therefore, a reasonable maximum purchase price could be 800 euros.