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

1. Current 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. Current Listing Price and Previous Prices: The current listing price is 425 euros. In previous auctions, hammer prices have varied, but generally, hammer prices for coins in similar conditions have ranged from 240 to 460 euros, depending on the condition and demand at that time.

3. Price Trends: Observing the hammer prices from previous auctions, it seems that coins with a condition rating of 85 to 95 have reached hammer prices ranging from 400 to 460 euros in recent years. This suggests that there is an active market and that prices may be increasing.

4. Average Hammer Price: The average hammer price for this coin is 319.19 euros, indicating that, although there are variations, the hammer price tends to be below the current listing price.

Based on these factors, an estimated maximum purchase price could be in the range of 450 to 500 euros, given that the condition is good and there is a price history supporting this estimate. However, it is important to consider the competition in the auction and the specific demand at the time.