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

1. Current condition: The coin has a condition of 90 (EF), which indicates that it is in good shape. This generally increases its value compared to coins with lower conditions.

2. Previous auction prices: By looking at the hammer prices of coins with similar conditions (around 90-95), we can see that the hammer prices have varied, but there are examples of auctions reaching up to 480 euros for conditions of 95.

3. Average hammer price: The average hammer price for this coin is 418.14 euros, which provides a good reference.

4. Starting price: The starting price is 380 euros, suggesting that the seller expects a reasonable price, but not necessarily the maximum.

5. Auction trends: The coin has been auctioned 17 times, with an 82% sell-through rate, indicating a consistent interest in the coin.

Based on these factors, an estimated maximum purchase price could be in the range of 480 to 550 euros, considering that the condition is good and there are precedents for hammer prices in that range. Therefore, a reasonable maximum purchase price could be 550 euros.