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. Starting Price: The starting price is 400 euros. This is the initial price expected to be obtained at the auction.

3. Previous Prices: By observing the hammer prices from previous auctions for coins with a similar condition (85), we can see that the hammer prices have varied. For example, in previous auctions, coins with a condition of 85 have reached hammer prices of up to 340 euros, but there are also examples of higher prices for similar conditions.

4. Recent Trends: In the most recent auctions, hammer prices for coins of similar condition have ranged from 360 to 400 euros, suggesting that interest in coins in good condition is increasing.

5. Average Hammer Price: The average hammer price for this coin is 323.88 euros, which can serve as a reference point.

Based on these factors, an estimated maximum purchase price could be in the range of 400 to 450 euros, considering that the condition is good and there is growing interest in such coins. However, since the starting price is 400 euros, it is likely that buyers will be willing to bid up to that limit or slightly above, depending on the competition in the auction.

Therefore, a reasonable maximum purchase price could be 450 euros.