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 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, coins with similar conditions have had hammer prices that varied, but many have exceeded 300 euros. For example, in recent auctions, coins with a condition of 90 have reached hammer prices of up to 456 euros.

3. Price Trends: By observing the hammer prices of similar coins in the past, it can be noted that the hammer price tends to be in a range of 300 to 450 euros, depending on demand and condition.

4. Average Hammer Price: The average hammer price for similar coins is 276.88 euros, but given that the condition of this coin is superior, it is reasonable to expect a higher hammer price.

5. Sales Expectations: Since there are 2 auctions scheduled in the coming days, this may increase competition and, therefore, the hammer price.

Taking all these factors into account, an estimated maximum purchase price for this coin could be around 450-500 euros, considering that the condition is good and there is interest in the coin. This also aligns with the hammer prices of recent auctions for coins of similar condition.