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

1. Coin 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 Auction Prices: By looking at the hammer prices of coins with similar conditions (85 and 90), we can see that the hammer prices have varied, but generally have remained in a range of 270 to 360 euros for conditions of 85 and 90.

3. Current Starting Price: The starting price is 400 euros, which suggests that the seller has high expectations for this auction.

4. Price Trends: In recent auctions, hammer prices for coins with similar conditions have been in the range of 300 to 400 euros, with some reaching up to 480 euros in exceptional conditions.

5. Competition Analysis: Given that there is significant interest in this coin (sold 324 times in the past), it is likely that there will be competition in the auction, which could drive up the hammer price.

Based on these factors, an estimated maximum purchase price for this coin could be between 350 and 400 euros, considering that the starting price is 400 euros and that the interest in the coin may lead to competitive bidding. However, if securing the purchase is desired, a limit of 380 euros could be a prudent strategy.