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

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

2. Previous Auction Prices: By looking at the hammer prices of coins with a similar condition (90) in the past, we can see that the hammer prices have varied, but there are recent examples showing hammer prices in the range of 320 to 380 euros.

3. Starting Price and Average Hammer Price: The current starting price is 375 euros, and the average hammer price in the past has been approximately 266.85 euros. However, since the starting price is relatively high, this suggests that bidders are willing to pay more for this particular coin.

4. Recent Trends: In the most recent auctions, hammer prices have shown an upward trend, especially for coins in good condition.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 400 to 450 euros. This is based on the condition, previous hammer prices, and the current market trend.