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

1. Condition of the coin: The coin to be auctioned has a condition rating of 90 (EBC), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Starting price and previous prices: The starting price is 400 euros. The average hammer price in previous auctions for this coin is 458.94 euros, suggesting that, in general, coins of this reference tend to sell for above their starting price.

3. Auction history: In the auction history, it is observed that coins with similar conditions have reached hammer prices that vary considerably, but there are examples of coins that have sold for significantly higher prices, especially those with superior conditions.

4. Recent trends: In the most recent auctions, hammer prices have been quite high, which could indicate an upward trend in interest for this coin.

Based on these factors, an estimated maximum purchase price could be in the range of 600 to 800 euros. This is based on the fact that the condition is good and that the price history shows that similar coins have reached hammer prices in that range. However, since the starting price is 400 euros, it is likely that the hammer price will not significantly exceed this range unless there is strong competition among bidders.

Therefore, a reasonable maximum purchase price could be 700 euros.